Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Protecting content from illicit reproduction by proof of existence of a
complete data set
This invention relates primarily to the field of consumer electronics, and in
particular to the protection of copy-protected content material.
The illicit distribution of copyright material deprives the holder of the
copyright legitimate royalties for this material, and could provide the
supplier of this illicitly
distributed material with gains that encourage continued illicit
distributions. In light of the
ease of information transfer provided by the Internet, content material that
is intended to be
copy-protected, such as artistic renderings or other material having limited
distribution rights,
are susceptible to wide-scale illicit distribution. The MP3 format for storing
and transmitting
compressed audio files has made the wide-scale distribution of audio
recordings feasible,
because a 30 or 40 megabyte digital audio recording of a song can be
compressed into a 3 or
4 megabyte MP3 file. Using a typical 56 kbps dial-up connection to the
Internet, this MP3
file can be downloaded to a user's computer in a few minutes. Thus, a
malicious party could
read songs from an original and legitimate CD, encode the songs into MP3
format, and place
the MP3 encoded song on the Internet for wide-scale illegitimate distribution.
Alternatively,
the malicious party could provide a direct dial-in service for downloading the
MP3 encoded
song. The illicit copy of the MP3 encoded song can be subsequently rendered by
software or
hardware devices, or can be decompressed and stored onto a recordable CD for
playback on a
conventional CD player.
A number of schemes have been proposed for limiting the reproduction of
copy-protected content material. The Secure Digital Music Initiative (SDMI)
and others
advocate the use of "digital watermarks" to identify authorized content
material. European
patent application EP 091901 "Embedding auxiliary data in a signal" discloses
a technique
for watermarking electronic material, and is incorporated by reference herein.
As in its paper
watermark counterpart, a digital watermark is embedded in the content material
so as to be
detectable, but unobtrusive. An audio playback of a digital music recording
containing a
watermark, for example, will be substantially indistinguishable from a
playback of the same
recording without the watermark. A watermark detection device, however, is
able to
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distinguish these two recordings based on the presence or absence of the
watermark. Because
some content material may not be copy-protected and hence may not contain a
watermark,
the absence of a watermark cannot be used to distinguish legitimate from
illegitimate
material. On the contrary, the absence of a watermark is indicative of content
material that
can be legitimately copied freely.
Other copy protection schemes are also available. For example, European
patent application EP0906700, "Method and system for transferring content
information and
supplemental information related thereto", presents a technique for the
protection of
copyright material via the use of a watermark "ticket" that controls the
number of times the
protected material may be rendered, and is incorporated by reference herein.
An accurate reproduction of watermarked material will cause the watermark to
be reproduced in the copy of the watermarked material. An inaccurate, or lossy
reproduction
of watermarked material, however, may not provide a reproduction of the
watermark in the
lossy copy of the material. A number of protection schemes, including those of
the SDMI,
have taken advantage of this characteristic of lossy reproduction to
distinguish legitimate
material from illegitimate material, based on the presence or absence of an
appropriate
watermark. In the SDMI scenario, two types of watermarks are.defined: "robust"
watermarks, and "fragile" watermarks. A robust watermark is one that is
expected to survive
a lossy reproduction that is designed to retain a substantial portion of the
original content
material, such as an MP3 encoding of an audio recording. That is, if the
reproduction retains
sufficient information to allow a reasonable rendering of the original
recording, the robust
watermark will also be retained. A fragile watermark, on the other hand, is
one that is
expected to be corrupted by a lossy reproduction or other illicit tampering.
In the SDMI scheme, the presence of a robust watermark indicates that the
content material is copy protected, and the absence or corruption of a
corresponding fragile
watermark when a robust watermark is present indicates that the copy protected
material has
been tampered with in some manner. An SDMI compliant device is configured to
refuse to
render watermarked material with a corrupted watermark, or with a detected
robust
watermark but an absent fragile watermark, except if the corruption or absence
of the
watermark is justified by an "SDMI-certified" process, such as an SDMI
compression of
copy protected material for use on a portable player. For ease of reference
and understanding,
the term "render" is used herein to include any processing or transferring of
the content
material, such as playing, recording, converting, validating, storing,
loading, and the like.
This scheme serves to limit the distribution of content material via MP3 or
other compression
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techniques, but does not affect the distribution of counterfeit unaltered
(uncompressed)
reproductions of content material. This limited protection is deemed
commercially viable,
because the cost and inconvenience of downloading an extremely large file to
obtain a song
will tend to discourage the theft of uncompressed content material.
It is an object of this invention to extend the protection of copy-protected
material to include the protection of uncompressed content material.
This object and others are achieved by selecting a sufficient number of data
items for
inclusion in a data set so as to discourage a transmission of the entire set
over a limited
bandwidth communications path, such as the Internet. Each portion of a data
set is bound to
the entirety of the data set so that portions of data sets that are
independently distributed can
be distinguished. In the case of audio recordings, for example, the data set
includes an entire
album, the individual songs on the album constituting portions of this data
set. By binding
each song to the album, a compliant player can be configured to refuse to
render items in the
absence of the complete data set. In this manner, the theft of a song requires
a theft of the
entire album. An uncompressed digital recording of an entire album consumes
hundreds of
megabytes of data, and the infeasibility or impracticality of downloading
hundreds of
megabytes of data is expected to provide sufficient discouragement for the
theft of
uncompressed content material. In a preferred embodiment, a watermark is
created for each
section of the data sent that contains an "entirety parameter" associated with
the data set. The
entirety parameter is a hash value that is based on a random number stored in
the watermarks
of each section. When presented for rendering, the entirety parameter is read,
and the
watermarks of a random selection of sections within the data set are compared
to this entirety
parameter to assure, with statistical certainty, that the entirety of the data
set is present.
The invention is explained in further detail, and by way of example, with
reference to the accompanying drawings wherein:
Fig. 1 illustrates an example system for protecting copy-protected content
material in accordance with this invention.
Fig. 2 illustrates an example data structure that facilitates a determination
of
the presence of an entirety of a data set in accordance with this invention.
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Fig. 3 illustrates an example flow diagram of an encoder that creates a data
set
and accompanying parameters to facilitate a determination of the presence of
an entirety of
the data set in accordance with this invention.
Fig. 4 illustrates an example flow diagram of a decoder that renders a data
item of a data set in dependence upon the presence of the entirety of the data
set in
accordance with this invention.
Throughout the drawings, the same reference numerals indicate similar or
corresponding features or functions.
The theft of an item can be discouraged by making the theft more time
consuming or inconvenient than the worth of the stolen item. For example, a
bolted-down
safe is often used to protect small valuables, because the effort required to
steal the safe will
typically exceed the gain that can be expected by stealing the safe.
The time required to download an MP3 encoding of an average song from the
Internet, using a 56 kbs modem, is about 15 minutes, depending upon the
network loading
and other factors. Although it may impossible to define a specific "worth" to
download time
durations, it is believed that many people would be willing to incur a 15-
minute download
duration to receive a song of interest. On the other hand, the time required
to download a
non-compressed digital recording of an average song, using a 56 kbs modem, is
about two
hours, and it is believed that few people would be willing to incur a two hour
download
duration to receive a song of interest. Although a person may occasionally
incur the two-hour
download time to receive a song, the likelihood of two hour downloads becoming
a prevalent
means for stealing a song is expected to be minimal. For this reason,
conventional protection
schemes have been based on the need to identify compressed copies of protected
material,
using, for example, the combination of robust and fragile watermarks discussed
above.
For ease of reference and understanding, the terms "lossless" and
"uncompressed" are used synonymously herein. As will be evident to one of
ordinary skill in
the art, this invention is independent of whether the communicated information
is
compressed or uncompressed, and independent of whether the compression is
lossy or
lossless. The terms "compressed" and "uncompressed" are used herein because
conventional
solutions exist for the detection of lossy encodings such as MP3, and it is
the degree of
compression that is achieved by the lossy encoding of MP3 that has made wide-
scale
distribution of protected material feasible. As is known in the art, lossless
compression
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schemes exist. Lossless compression schemes, however, do not achieve the
reduction in data
that common lossy compressions achieve, and are not considered sufficiently
"compressed"
to be distinguished from "uncompressed" for the purposes of understanding this
invention.
Also for ease of understanding, the invention is presented herein in the
context
5 of digitally recorded songs that are downloadable from the Internet. As will
be evident to one
of ordinary skill in the art, the invention is applicable to any recorded
information that is
expected to be transmitted via a limited bandwidth communications path. For
example, the
individual content material items may be data records in a larger database,
rather than songs
of an album.
The likelihood of a person illicitly downloading a song can be expected to be
inversely proportional to the time required to effect the download. This
invention is premised
on the assumption that there is some threshold download duration above which
the expected
loss of revenue caused by illicit downloads is deemed acceptable. Experiments
and surveys
can be performed to determine a download duration that is sufficient to
discourage the illicit
download of a song, or, such a discouraging-duration can be estimated and will
likely be in
the order of 1/a to 1 hour. That is, it is likely that "many" illicit
downloads of a popular song
will occur if the duration is less than a half hour, and "few" illicit
downloads will occur if the
duration is greater than an hour, even if the song is very .popular.
As technology advances, and alternative communication schemes become
available, the time required to download an uncompressed file can be expected
to decrease.
Using a DSL or cable connection to the Internet, for example, reduces the time
required to
communicate an uncompressed digital song to less than 5 minutes, depending on
network
loading and other factors. As noted above, most existing protection schemes
are not able to
distinguish lossless copies of digital data from the original copy. Therefore,
in a high-speed
data transfer environment, the likelihood of lost revenue due to illicit
downloads of
uncompressed digital songs can be expected to increase significantly.
In accordance with this invention, individual songs on a compact disc (CD), or
other medium, are bound to the entire contents of the CD, and a compliant
playback or
recording device is configured to refuse to render an individual song in the
absence of the
entire contents of the CD. The time required to download an entire album on a
CD in
uncompressed digital form, even at DSL and cable modem speeds, can be expected
to be
greater than an hour, depending upon network loading and other factors. Thus,
by requiring
that the entire contents of the CD be present, at a download "cost" of over an
hour, the
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likelihood of a theft of a song via a wide-scale distribution on the Internet
is substantially
reduced.
Fig. 1 illustrates an example block diagram of a protection system 100 in
accordance with this invention. The protection system 100 comprises an encoder
110 that
encodes content material onto a medium 130, and a decoder 120 that renders the
content
material from the medium 130. The encoder 110 includes a selector 112 that
selects content
material from a source, and a recorder 114 that records this material onto the
medium 130.
The selector 112, for example, may be configured to select content information
corresponding to songs that are being compiled into an album. The recorder 114
appropriately formats, encodes, and stores the information on the medium 130,
using
techniques common in the art.
In accordance with this invention, the encoder 110 includes a binder 116 that
binds each item selected by the selector 112 to the entirety of the
information that is recorded
onto to the medium 130 by the recorder 114. In general terms, the information
stored on the
medium 130 constitute data items, the entirety of the information stored on
the medium 130
forms a data set, and each data item is bound to the data set.
The decoder 120 in accordance with this invention comprises a renderer 122
and a gate 124 that is controlled by an entirety checker 126. The renderer 122
is configured to
retrieve information from a medium reading device, such as a CD reader 132. As
is common
in the art, the renderer 122 retrieves the information by specifying a
location index, and in
response, the reader 132 provides the data located at the specified location
index on the
medium 130. Block reads of data at contiguous locations on the medium 130 are
effected by
specifying a location index and a block size.
The dotted lines of Fig. 1 illustrate an example song extractor 142 that
extracts
a song from the medium 130 and communicates it to an example CD imitator 144,
representative of a possible illicit download of the song via the Internet.
The CD imitator 144
represents, for example, a software program that provides information in
response to a
conventional CD-read command. Alternatively, the information received from the
song
extractor can be written to a CD medium, and provided to the conventional CD
reader 132.
As noted above, the song extractor 142 is likely to be used because the
transmission of the
entirety of the contents of the medium 130 is assumed to be discouraged by the
purposeful
large size of the contents of the medium 130.
In accordance with this invention, the entirety checker 126 is configured to
obtain data from the medium 130, typically via the renderer 122, to determine
whether the
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entire data set is present. Any number of a variety of techniques, common in
the art, can be
used to verify the presence of an entirety of the data set. For example, a
checksum
corresponding to the data items in the data set can be used to verify that all
the data items are
present, by computing a checksum on the data items available to the renderer
112, and
comparing this checksum to the checksum corresponding to the original entirety
of the data
set. This checksum can be digitally signed, communicated with the data set,
and subsequently
certified using a cryptographic key.
In the context of consumer devices such as audio CD playback devices, a
checksum-based approach may not be feasible. Audio CD players include error-
correcting
and other decoding schemes that allow for a variance with each reading of the
CD. Audio CD
players do not, for example, necessarily start a playback of a song at
precisely the same point.
Similarly, if an error is detected while the CD is being read, a repetition of
a prior section is
often substituted for the erroneous section. A variance of a few bytes in the
start of a song, or
the repetition of a millisecond's worth of bytes, will not cause a noticeable
audible difference,
but the presence or absence of these bytes will have a significant effect on a
checksum
associated with the song.
Watermarks, and the corresponding watermark detection equipment, are
configured to provide an accurate and repeatable reading of the watermark
under a variety of
circumstances. For example, a watermark is typically recorded at a
substantially lower bit
rate than the bit rate of the recorded audio signal, and redundant recordings
of the watermark
are used to further improve the likelihood that an accurate value is read as
the watermark. As
noted above, the robustness of a watermark can be varied, typically by varying
the bit rate
and redundancy of the recording of the watermark. Even a "fragile" watermark
is typically
configured to survive minor variances and anomalies that are common in the
reading of
information from a conventional consumer CD playback device. As used herein,
the term
watermark includes one or more watermark encodings; a watermark may include,
for
example, a fragile component and a robust component. Depending upon the
watermark
production method, these components may be embedded in the section
independently, or as a
common entity. For ease of understanding, the terms watermark, fragile
watermark, and
robust watermark are used herein independent of the method of collecting or
segregating
individual components during the watermark production process.
Fig. 2 illustrates an example data structure 200 for storing data items in a
data
set that facilitates a verification that the entirety of the original data set
is present. A track 2I0
arid section 220 structure is illustrated, consistent with the memory
structure of conventional
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CD and other storage media. In a preferred embodiment, the data set is self-
referential: the
data set contains one or more parameters that can be used to verify the
presence of the other
members of the data set. In the example data structure 200, a random value
R(i) 234 is
assigned to each section 220 of the data set. A hash H(R(i)) of each of these
random values
R(i) is stored on the medium preferably as "out of band" data (OBD) 240. This
data 240, for
example, may be stored within the Table of Contents of a typical CD, as "CD-
ROM" data in
a mixed audio-data CD, as a separate and unique data section, as a false song
containing only
data, and so on. A hash of a composite of the hashes H(H(RO), H(R1), ...
H(Rn)) 240 is used
as a check value CHK that identifies the entirety of the data set. The check
value CHK 232
and the random value R(i) 234 form the watermark 230 that is associated with
each section
220 of the data set. That is, in a preferred embodiment, the CD 130 of FIG. 1
is created with
each recorded section 220 having a watermark 230 that includes an identifier
CHK 232 of the
entirety of the data set on the CD, and an identifying random number 234 of
the section 220.
Hash values are used because, in general, a hash computation is irreversible.
The value used
I5 to produce the hash value cannot be determined, and the effects of a change
of one or more of
the items used to form the hash value also cannot be determined. (The term
"cannot be
determined" is used herein in the cryptographic sense: a determination of the
value can be
expected to consume more time and resources than is practical to pursue.) The
section
watermarks may be robust or fragile watermark. In a preferred embodiment, the
check value
CHK 232 is encoded as a robust watermark, to assure an identification of the
material as
protected material, and the random number R(i) 234 is encoded as a fragile
watermark. As
discussed above, a robust watermark is recorded at a lower bit rate or with
more redundancy
than a more fragile watermark. Alternatively stated, a fragile watermark
consumes less
resources than a robust watermark. Also as discussed above, a fragile
watermark provides an
indication of other forms of tampering, such as the compression of the
protected data. The
check value CHK may also be a portion, such as the lower m bits, of the hash
of the
composite. Although the security of a partial hash value is less than that of
a complete hash
value, the savings in resources to store this value may justify this reduction
in security.
Fig. 3 illustrates an example flow diagram for an encoder 110 that creates a
data set on a medium in accordance with this invention. At 310, a data item is
selected for
inclusion in the data set. This data item may be a song that is selected for
inclusion in an
album, a data record that is selected for inclusion in a database, and so on.
The data item
contains one or more data sections. For example, a song may be partitioned
into a plurality of
equal time-duration sections, each data record may form a single section, etc.
A random
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number R(i) is assigned to each section of the data item, at 320, and the size
of the data item
is added to an accumulated size of the entirety of the data set, at 330. In
accordance with this
invention, data items are added to the data set until the size of the data set
is deemed large
enough to discourage a subsequent transmission of the data set via a limited
bandwidth
communications channel. This "discouraging size" is a subjective value, and
will depend
upon the assumed available communications bandwidth, the loss incurred by the
transmission, and so on. If the discouraging size has not been reached, at
335, another data
item is selected for inclusion in the data set, via the branch back to block
310. Not illustrated
in the example flow diagram of Fig. 3, other criteria may also be used to
determine whether
to add additional data items to the data set. For example, if the data items
correspond to songs
of an existing album collection, all of the songs will typically be added to
the data set,
regardless of whether the size of the data set has exceeded the determined
discouraging size.
If all of the songs of the album collection have been selected, and the
discouraging size
criterion has not yet been reached, other data items are selected to
accumulate the required
discouraging size. For example, data items comprising random data bits may be
added to the
data set to increase its size. These random bits will typically be stored as
out of band data,
CD-ROM data, and the like, to prevent it from being rendered as audible sounds
by a
conventional CD player. Alternatively, the data items may comprise other
sample songs that
are provided to encourage the sale of other albums, or images and video
sections related to
the recorded content material. Similarly, promotional material, such as
Internet access
subscription programs may also be included in the recorded information on the
recorded
medium. These and other means of adding size to a data set will be evident to
one of ordinary
skill in the art in view of this invention. In accordance with this invention,
each of the
selected data items are bound to the data set, such that a removal or
alteration of any of the
data items, including any random sections, promotional material, and the like
that were added
to increase the size of the data set, can be used to preclude the subsequent
rendering of data
items from this data set.
After the data items are selected to provide a sufficiently sized data set, a
check value CHK is computed, based on a composite of the random numbers that
were
assigned to the sections of each data item, at 340. This composite may
include, for example, a
checksum corresponding to the random numbers, a checksum corresponding to a
function,
such as a hash function, of each random number, and so on. As discussed above,
this CHK
value is preferably a hash of the composite of the random values, or a portion
of such a hash.
At 350, a watermark is created for each section of the data set that includes
this CHK value
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and also includes the random number R(i) that is assigned to the section. As
noted above, the
CHK value is preferably encoded as a robust watermark, and the random number
as a fragile
watermark. Each section is recorded onto the medium with this composite
watermark, at 360,
and a hash of each section's random number is stored onto the medium, at 370,
preferably as
5 Out of Band Data (OBD). In this manner, the individual data items are bound
to the entirety
of the data set, via the CHK value, and the validity of this entirety value
can be verified via
the self-referential hash values of the random numbers that were used to
create the CHK
value. Other encoding schemes that bind the individual data items to the data
set will be
evident to one of ordinary skill in the art in view of this disclosure.
10 Fig. 4 illustrates an example flow diagram for a decoder 120 that is
configured
to render a selected data item, such as a selected song, in dependence upon
the presence of
the entirety of the data set associated with this data item. This flow diagram
assumes that the
encoding method of Fig. 3 had been used to create the original copy of the
data item and data
set. If another binding scheme is used, one of ordinary skill in the art will
be able to
appropriately modify the example flow diagram of Fig. 4 in view of this
example
embodiment. It is assumed that the flow of Fig. 4 is invoked upon a
determination that the
selected data item is a copy-protected item, via, for example, a detection of
a copy-protect
watermark or other identifying mechanism. At 410, the hashed values of the
random numbers
associated with each section of the data items in the data set are read from
the medium, which
may be a reading from the true copy (130 of Fig. 1) of the recorded content
material, or from
an illicit source (144 of Fig. 1). At 420, a hash is computed based on a
composite of these
hash values, using the same algorithm that is used at 340 of FIG. 3 to create
the CHK value
that is contained in the watermark of each section of a true copy of the
content material. A
random section of the data set is selected, at 430, and the check value of the
watermark is
read, as CHK', at 440. Alternatively, the first section that is selected for
verification may be a
section from within the data item selected for rendering, to immediately
verify that the
selected data item is part of the original data set. In the context of a
recorded song, the data
section typically corresponds to a fifteen second section of the song. If the
computed check
value CHK is not equal to the read check value CHK', at 445, indicating a
modification to
the collection of hashes of the random numbers, the decoder is configured to
refuse to render
the content material, at 480.
To verify that the data section has not been substantially modified, the
random
number assigned to the randomly selected section Sx is read, as R'(x), at 450.
As discussed
above, the random number is preferably stored as a fragile watermark, and a
characteristic of
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a fragile watermark is that a substantial modification to the data containing
the watermark
causes a corruption or destruction of the fragile watermark. A hash of the
read random value
H(R'(x)) is also computed at 450, and this hash H(R'(x)) is compared to the
corresponding
hash value H' (R(x)) that was read at block 410 and subsequently used to
create the
verification check value CHK. If these hash values do not match, at 455, the
decoder is
configured to refuse to render the content material, at 480. If these hash
values match, other
sections may be similarly tested, via the loop 465-430 until sufficient
confidence is gained
that the content material has not been substantially modified from the true
copy. In a
preferred embodiment, only one or two sections axe tested, so as to minimize
the delay
introduced by this data-set-entirety verification procedure. When sufficient
confidence is
gained, at 465, that the entirety of the data set is present, the selected
song is rendered, at 470.
As will be evident to one of ordinary skill in the art, additional
verification checks can
subsequently be applied. Preferably, the watermark of each section of the
selected song is
verified as each section of the song is read, to verify that each section of
the song is a valid
member of the original data set, by checking that each CHK' value contained in
each section
corresponds to the verification check value CHK.
The foregoing merely illustrates the principles of the invention. It will thus
be
appreciated that those skilled in the art will be able to devise various
arrangements which,
although not explicitly described or shown herein, embody the principles of
the invention and
are thus within its spirit and scope. For example, the examples presented
above illustrate each
part of the recorded material being part of the data set. In an alternative
embodiment, select
data items, or select parts of data items, may be used to form the data set,
for efficiency
purposes. For example, the tail end of songs may not be part of the "data set"
as defined
herein, because the watermark process may be based on a fixed block-size for
each
watermark, or each redundant copy of the watermark. If, for example, the
watermark, or
other parameter, requires ten seconds of a recording for a reliable embedding,
the remainder
of ((the song's length) modulo (10 seconds)) will be recorded on the medium,
but not
included in the "data set" whose entirety is being checked. In like manner,
some promotional
material may be included on the recorded medium, but purposely excluded from
the data set,
so that it may be freely copied and rendered elsewhere. Note also that the
example flow
diagrams are presented for ease of understanding, and the particular
arrangement and
sequence of steps are presented for illustration. For example, simple
equalities are illustrated
in the decision blocks for determining correspondence, whereas depending upon
the
particular techniques used to encode or decode the parameters, the assessment
as to whether
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the read item corresponds to a determined item can include a variety of
intermediate
processes. These processes may include, for example, a decryption of items
based on
particular keys, fuzzy logic or statistical testing to determine if two values
are "close enough"
to imply a correspondence, and the like. Variations such as these and others
will be evident to
one of ordinary skill in the art in view of this invention, and are included
in the spirit and
scope of the following claims.
