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<br>
Chapters:
<br>
<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
<a href="InvokingGri.html">3: Invocation</a><br>
<a href="GettingMoreControl.html">4: Finer Control</a><br>
<a href="X-Y.html">5: X-Y Plots</a><br>
<a href="ContourPlots.html">6: Contour Plots</a><br>
<a href="Images.html">7: Image Plots</a><br>
<a href="Examples.html">8: Examples</a><br>
<a href="Commands.html">9: Gri Commands</a><br>
<a href="Programming.html">10: Programming</a><br>
<a href="Environment.html">11: Environment</a><br>
<a href="Emacs.html">12: Emacs Mode</a><br>
<a href="History.html">13: History</a><br>
<a href="Installation.html">14: Installation</a><br>
<a href="Bugs.html">15: Gri Bugs</a><br>
<a href="TestSuite.html">16: Test Suite</a><br>
<a href="GriInThePress.html">17: Gri in Press</a><br>
<a href="Acknowledgments.html">18: Acknowledgments</a><br>
<a href="License.html">19: License</a><br>
<br>
Indices:<br>
<a href="ConceptIndex.html"><i>Concepts</i></a><br>
<a href="CommandIndex.html"><i>Commands</i></a><br>
<a href="BuiltinIndex.html"><i>Variables</i></a><br>
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<h2>10.5: Synonyms</h2>
Synonyms are used by Gri to store character strings. Gri denotes
synonyms with words beginning with backslash (e.g., `<font color="#82140F"><code>\syn</code></font>'),
following the TeX convention.
<p>
<UL>
<LI><a href="Synonyms.html#NamingConvention">Naming Convention</a>: Their names with a backslash, e.g. `<font color="82140F"><code>\syn</code></font>'
<LI><a href="Synonyms.html#UsingSynonyms">Using Synonyms</a>: Some usage examples
<LI><a href="Synonyms.html#ImportantBuiltinSynonyms">Important Builtin Synonyms</a>: e.g. `<font color="82140F"><code>\.command_file.</code></font>'
<LI><a href="Synonyms.html#AliasSynonyms">Alias Synonyms</a>: e.g. `<font color="82140F"><code>\@alias</code></font>'
<LI><a href="Synonyms.html#LocalSynonyms">Local Synonyms</a>: Working with the arguments of newcommands
</UL>
<!-- @node Naming Convention, Using Synonyms, Synonyms, Synonyms -->
<a name="NamingConvention" ></a>
<h3>10.5.1: Naming convention for synonyms</h3>
Synonym names begin with a backslash (e.g., `<font color="#82140F"><code>\filename</code></font>'). After
the backslash, Gri expects a letter (upper or lower case) or one or more
periods. Following this is an arbitrary string of letters, numbers, or
underscores. If there are periods at the start, then the same number of
periods must be used at the end. The following are some examples
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\simple = "Howdie"
\.longer_example. = "Dots and underscores are ok too"
\a2 = "OK for number at end ..."
\a3bb = "... and inside"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Gri defines several synonyms for its own use, so that if you modify
these, you may get strange results. Each of these starts and ends with
a single period.
<p>
There is an exception to the above rule, one which mostly comes up when
using netCDF files which may have variable names that may contain
punctuation. Gri permits synonym names to have punctuation characters
(but not blanks or tabs) in synonym names, provided that the second
character in the name is an opening brace and that the last character is
a closing brace, e.g.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\{foo.bar} = "Foo bar"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
This is used particularly for files in the netCDF format,
for reading variable attributes, which by netCDF convention use a colon
(`<font color="82140F"><code>:</code></font>') to separate variable name and attribute name (see <a href="Read.html#ReadSynonymorVariable">Read Synonym or Variable</a>). For more information on netCDF format, see
<p>
`<font color="#82140F"><code>http://www.unidata.ucar.edu/packages/netcdf/index.html</code></font>'
<a href="http://www.unidata.ucar.edu/packages/netcdf/index.html">
here </a>.
<p>
Synonyms may be freely embedded in strings (a common example is
`<font color="#82140F"><code>draw title "Data from file `\datafile'"</code></font>'. They may also appear
anywhere in commands (e.g., `<font color="#82140F"><code>open \filename</code></font>'). The exception to
this rule is that Gri ignores your synonyms within math mode, in order
to prevent clashes (e.g. you might define `<font color="#82140F"><code>\alpha</code></font>' as a synonym
storing the value `<font color="#82140F"><code>"foo bar"</code></font>', but Gri will ignore this within
math-mode, so that `<font color="#82140F"><code>$\alpha$</code></font>' will still mean the Greek letter
alpha).
<p>
To get a backslash in a string without Gri thinking it is part of a
synonym, use two backslashes (e.g.,
`<font color="#82140F"><code>show "The backslash character \\ is used for synonyms."</code></font>'). This
may sometimes be required in
`<font color="#82140F"><code>system</code></font>'
commands (see <a href="System.html#System">System</a>), to prevent Gri from converting
substrings like `<font color="#82140F"><code>\n</code></font>' (which many system commands use to represent
the newline character). For example, the command
`<font color="#82140F"><code>system perl -e 'print "foo\nbar";'</code></font>' will be mangled if Gri has
already been told that
`<font color="#82140F"><code>\nbar</code></font>' is a synonym. (There will be no problem if `<font color="#82140F"><code>\nbar</code></font>' is
not an existing synonym, since Gri will then just leave it in place.)
To be sure that no mangling can occur, replace each backslash with two
backslashes. This tells Gri not to try to substitute a synonym at that
location. In the example below, the first system call prints
`<font color="#82140F"><code>fooled you!</code></font>' on one line line, because Gri substituted for what it
thought was a synonym called `<font color="#82140F"><code>\nbar</code></font>'; the second (correctly) prints
`<font color="#82140F"><code>foo</code></font>' on one line and `<font color="#82140F"><code>bar</code></font>' on the next.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\nbar = "led you!"
system perl -e 'print "foo\nbar\n";'
system perl -e 'print "foo\\nbar\\n";'
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Similarly, if your system command is expecting to see `<font color="#82140F"><code>\t</code></font>' (for a
tab character), then you must write `<font color="#82140F"><code>\\t</code></font>' to prevent Gri from
trying to substitute a synonym named `<font color="#82140F"><code>\t</code></font>'.
<p>
The `<font color="#82140F"><code>show</code></font>' command has a special syntax for permitting newlines and
tabs in strings (see <a href="Show.html#Show">Show</a>).
<p>
<!-- @node Using Synonyms, Generalizing Code, Naming Convention, Synonyms -->
<a name="UsingSynonyms" ></a>
<h3>10.5.2: Some uses for synonyms</h3>
Synonyms store strings and are useful for anything strings are useful
for, e.g. filenames, plot labels, names of variables, etc.
<p>
<UL>
<LI><a href="Synonyms.html#GeneralizingCode">Generalizing Code</a>:
<LI><a href="Synonyms.html#StoringOSOutput">Storing OS Output</a>:
<LI><a href="Synonyms.html#StoringUserResponses">Storing User Responses</a>:
<LI><a href="Synonyms.html#StoringFileContents">Storing File Contents</a>:
<LI><a href="Synonyms.html#ExtractingWordsFromStrings">Extracting Words From Strings</a>:
</UL>
<!-- @node Generalizing Code, Storing OS Output, Using Synonyms, Using Synonyms -->
<a name="GeneralizingCode" ></a>
<h4>10.5.2.1: Using synonyms to generalize code</h4>
Synonyms are often used to store filenames, since then only a single
line of a file may need to be altered, in order to work with another
file, e.g.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\filename = "columns.dat"
open \filename
# a lot more code using the file name
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<!-- @node Storing OS Output, Storing User Responses, Generalizing Code, Using Synonyms -->
<a name="StoringOSOutput" ></a>
<h4>10.5.2.2: Using synonyms to store OS output</h4>
Synonyms provided a convenient way to store information from the OS.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
# Show the date.
\date = system date
show "Time is \date"
<p>
# Show the command file name, then use the system
# to construct a filename with the same beginning
# but ".dat" as the ending instead of ".gri".
show "The commandfile name is \.command_file."
\fn = system echo `basename \.command_file. .gri`.dat
show "A filename constructed from this is \fn"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
This example uses the Unix system commands `<font color="#82140F"><code>echo</code></font>' and
`<font color="#82140F"><code>basename</code></font>' to construct a filename ending in `<font color="#82140F"><samp>.dat</samp></font>', from the
command file name (stored in the builtin string `<font color="#82140F"><code>\.command_file.</code></font>'),
assuming that the command file name ends in `<font color="#82140F"><samp>.gri</samp></font>'.
<p>
NOTE: As usual, if the system command contains the Gri comment
designator (the string `<font color="#82140F"><code>#</code></font>'), protect it with double-quotes
(see <a href="System.html#System">System</a>).
<p>
<!-- @node Storing User Responses, Storing File Contents, Storing OS Output, Using Synonyms -->
<a name="StoringUserResponses" ></a>
<h4>10.5.2.3: Storing user responses via `<font color="#82140F"><code>query</code></font>'</h4>
You can ask the user for the contents of strings:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
query \filename "What's the data file?" ("file.dat")
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
The prompt `<font color="#82140F"><code>What's the name of the data file?</code></font>' is typed to the
terminal, and whatever string the user types is inserted into the
synonym `<font color="#82140F"><code>\filename</code></font>'. If the user types nothing, but simply presses
carriage return, the (optional) default string (which must be enclosed
in parentheses as shown) is put into `<font color="#82140F"><code>\filename</code></font>'. Note that the
default is ignored if it is not written properly: it must be enclosed in
double quotes enclosed in parentheses, with no intervening spaces.
<p>
<!-- @node Storing File Contents, Extracting Words From Strings, Storing User Responses, Using Synonyms -->
<a name="StoringFileContents" ></a>
<h4>10.5.2.4: Storing File Contents</h4>
You can read the contents of synonyms from a file:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
open \directory_file
read \file_name
close
open \file_name
read columns x y
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
The first (space-separated) word is read into the the first synonym after
the `<font color="#82140F"><code>read</code></font>' command, the second word into the second synonym, and so on.
If the word you want is not near the front of the line, you can use the command
`<font color="#82140F"><code>read line</code></font>' to get the whole line, then use the method described above
to extract the word you want. Indexing begins with 0, remember.
<p>
<!-- @node Extracting Words From Strings, Important Builtin Synonyms, Storing File Contents, Using Synonyms -->
<a name="ExtractingWordsFromStrings" ></a>
<h4>10.5.2.5: Working with words within strings</h4>
Sometimes a synonym will contain several words that you need to work
with indidually (e.g. it might contain a list of files that should be
processed). There are two ways to do this.
<p>
<dl>
<p>
<p>
<dt> <i>The `<font color="#82140F"><code>word of</code></font>' syntax.</i>
<dd><TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\sentence = "This sentence has five words"
\first_word = word 0 of "\sentence"
\last_word = word 4 of "This sentence has five words"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<p>
<dt> <i>The `<font color="#82140F"><code>[]</code></font>' syntax</i>
<dd>Individual words of synonyms may be accessed by prefixing the synonym
name with the index number of the word (starting at 0) enclosed in
square brackets.
<p>
The number in the square brackets may be a constant, a variable, or a
synonym, but not a more complicated expression. If the index value is a
floating-point number, it is first rounded to the nearest integer. If
the index value is negative or exceeds the number of words minus 1, then
an empty string is retrieved.
<p>
If <b>no number</b> appears in the square brackets, the result is the
number of words in a synonym.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\syn = "This has 4 words in it"
show "\[0]syn ... gives 'This'"
show "\[1]syn ... gives 'has'"
.i. = 3
show \[.i.]syn ... gives 'words'"
\i = "3"
show \[\i]syn ... gives 'words'"
show "\[]syn ... gives '6', i.e. number of words"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
</dl>
<!-- @node Important Builtin Synonyms, Alias Synonyms, Extracting Words From Strings, Synonyms -->
<a name="ImportantBuiltinSynonyms" ></a>
<h3>10.5.3: Some important builtin synonyms</h3>
<!-- latex: \index{@code{\.return_value.}, Return value} -->
<!-- latex: \index{@code{\.ps_file.}, PostScript file name} -->
<!-- latex: \index{@code{\.readfrom_file.}, data file name} -->
<!-- latex: \index{@code{\.command_file.}, command-file name} -->
<!-- latex: \index{@code{\.missingvalue.}, command-file name} -->
<!-- latex: \index{@code{\.home.}, home directory} -->
<!-- latex: \index{@code{\.system.}, operating system name} -->
<!-- latex: \index{@code{\.user.}, user's login name} -->
<!-- latex: \index{@code{\.time.}, time and date} -->
<!-- latex: \index{@code{\.wd.}, working directory} -->
<!-- latex: \index{@code{\.version.}, version of Gri} -->
<!-- latex: \index{@code{\.pid.}, process ID of job} -->
Within mathematics mode (portions of strings enclosed within
dollar-signs), Gri stores the definitions of many Greek letters and
mathematical symbols as math-mode synonyms (see <a href="MathematicalText.html#MathematicalText">Mathematical Text</a>).
<p>
Global synonyms are shared among commands. To see the built-in global
synonyms (see <a href="BuiltinIndex.html#IndexofBuiltins">Index of Builtins</a>)
use `<font color="#82140F"><code>show synonyms</code></font>', which
produces output that looks something like the following.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
Synonyms...
\.missingvalue. = "10000000000000000000000.000000"
\.return_value. = ""
\.version. = "2.7.0"
\.pid. = "3043"
\.wd. = "/home/kelley"
\.time. = "Sun May 20 13:18:32 2001"
\.user. = "kelley"
\.host. = "Intrusion.phys.ocean.dal.ca"
\.system. = "unix"
\.home. = "/home/kelley"
\.lib_dir. = "/usr/share/gri"
\.command_file. = "stdin"
\.readfrom_file. = "stdin"
\.ps_file. = "gri-00.ps"
\.path_data. = "."
\.path_commands. = "."
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
These things will be obvious to unix users; for example
`<font color="#82140F"><code>\.pid.</code></font>' is the process ID of the job (often used in names for
temporary files), and `<font color="#82140F"><code>\.wd.</code></font>' is the working directory (often used
in `<font color="#82140F"><code>draw title</code></font>' commands to indicate in which directory the gri job
was run.
<p>
Some commands set `<font color="#82140F"><code>\.return_value.</code></font>' to non-blank; the
meaning of the return value varies from command to command.
<p>
<!-- @node Alias Synonyms, Local Synonyms, Important Builtin Synonyms, Synonyms -->
<a name="AliasSynonyms" ></a>
<h3>10.5.4: Alias synonyms: the `<font color="#82140F"><code>\@alias</code></font>' syntax</h3>
Sometimes you need to work with a variable or a synonym whose name can
only be determined at run-time, perhaps through interaction with the
user, examination of a datafile, or examination of the command provided
to the OS when invoking Gri.
<p>
Gri handles this by so-called "alias" synonyms, which store the names of
other items.
<p>
The syntax is simple. Suppose that a synonym, called `<font color="#82140F"><code>\pointer</code></font>'
say, contains the <b>name of</b> another synonym, or a variable. Then
you may use `<font color="#82140F"><code>\@pointer</code></font>' anyplace you would normally use the item
named.
<p>
<dl>
<p>
<dt> <i>Illustrations of using the value of a named item</i>
<dd>The following prints an approximation to Pi followed by the name of
movie star.
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.pi. = 3.14
\pi_pointer = ".pi."
show \@pi_pointer # just like 'show .pi.'
<p>
\hero = "Gregory Peck"
\our_hero = "\\hero"
show "\@our_hero" # just like 'show "\hero"'
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<p>
<dt> <i>Illustrations of assigning to a named item</i>
<dd>The following prints an approximation to 2*Pi and yet another star; the
point is that the alias appears to the left of an assignment operator.
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
# Print approximation to 2*Pi
.pi. = 3.14
\pi_pointer = ".pi."
\@pi_pointer *= 2
show .pi.
<p>
# Stars don't shine alone
\hero = "Gregory Peck"
\our_hero = "\\hero"
\@our_hero = "Harrison Ford"
show "\hero"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
</dl>
<!-- @node Local Synonyms, If Statements, Alias Synonyms, Synonyms -->
<a name="LocalSynonyms" ></a>
<h3>10.5.5: Local synonyms</h3>
<!-- latex: \index{@code{\.proper_usage.}} -->
<!-- latex: \index{@code{\.words.}} -->
<!-- latex: \index{@code{\.word0.}} -->
<!-- latex: \index{@code{\.word1.}} -->
Local synonyms are created by Gri upon entry to a Gri command. You use
them to parse the command line that was used in calling the new command,
to look for options, gather filenames, etc. Local synonyms are known
only from within the local Gri command. They are not listed by
`<font color="#82140F"><code>show synonyms</code></font>', but they can be used freely in commands like
`<font color="#82140F"><code>show "Number of words is \.words."</code></font>'.
<p>
<ul>
<li>
Within any new Gri command, the number of words in the line that called
the command is available in `<font color="#82140F"><code>\.words.</code></font>'. The RPN operator `<font color="#82140F"><code>wordc</code></font>'
also yields the same value (see <a href="SolitaryOperators.html#SolitaryOperators">Solitary Operators</a>).
<li>
The first word in the calling line is `<font color="#82140F"><code>\.word0.</code></font>', the second
`<font color="#82140F"><code>\.word1.</code></font>', etc. (Note that this is the C convention, <b>not</b> the
FORTRAN convention. If `<font color="#82140F"><code>\.words.</code></font>' is 2, then `<font color="#82140F"><code>\.word0.</code></font>' and
`<font color="#82140F"><code>\.word1.</code></font>' are defined, but `<font color="#82140F"><code>\.word2.</code></font>', which FORTRAN programmers
expect, will not be defined.) If you don't know the place of the synonym
in advance (i.e. 0 versus 1, for `<font color="#82140F"><code>\.word0.</code></font>' versus `<font color="#82140F"><code>\.word1.</code></font>'),
then use the RPN operator `<font color="82140F"><code>wordv</code></font>' instead (see <a href="UnaryOperators.html#UnaryOperators">Unary Operators</a>).
<li>
Within any new Gri command, the proper calling usage is available in
`<font color="#82140F"><code>\.proper_usage.</code></font>'. This is useful in tests of syntax
(see <a href="NewCommands.html#AddingNewCommands">Adding New Commands</a>). For example:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
`draw depths from \file'
Draw depth data stored in indicated file. If the
filename contains periods or slashes, you'll
have to enclose it in double quotes, as
in the second example:
draw depths from file upper_cove
draw depths from file ../old_data/upper_cove
{
if {rpn \.words. 4 !=}
show "FATAL ERROR in `\.proper_usage.':"
show " Need 4 words; got \.words. words."
quit
end if
# Right number of words, so continue onward...
}
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
</ul>
These synonyms help you scan for optional words in commands. Suppose
you have defined a new command `<font color="#82140F"><code>New Thing [option]</code></font>'. If you call
it with `<font color="#82140F"><code>New Thing</code></font>', then (within `<font color="#82140F"><code>New Thing</code></font>') `<font color="#82140F"><code>\.words.</code></font>'
will be `<font color="#82140F"><code>"2"</code></font>', `<font color="#82140F"><code>\.word0.</code></font>' will be `<font color="#82140F"><code>"New"</code></font>' and `<font color="#82140F"><code>\.word1.</code></font>'
will be `<font color="#82140F"><code>"Thing"</code></font>'. On the other hand, if you call it with
`<font color="#82140F"><code>New Thing 22.3</code></font>' then `<font color="#82140F"><code>\.words.</code></font>' will be `<font color="#82140F"><code>3</code></font>',
`<font color="#82140F"><code>\.word0.</code></font>' will be `<font color="#82140F"><code>"New"</code></font>', `<font color="#82140F"><code>\.word1.</code></font>' will be
`<font color="#82140F"><code>"Thing"</code></font>' as before, and `<font color="#82140F"><code>\.word2.</code></font>' will be `<font color="#82140F"><code>"22.3"</code></font>'.
<p>
<b>EXAMPLE</b> Here is a new command to label lines drawn by
`<font color="#82140F"><code>draw curve</code></font>':
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
`Draw Label For Last Curve "label"'
Draw a label for the last curve drawn, using
..xlast.. and ..ylast.. built-in variables.
{
new .draw_label_for_last_curve_graylevel.
.draw_label_for_last_curve_graylevel. = ..graylevel..
set graylevel 0
draw label "\.word5." at \
{rpn ..xlast.. xusertocm 0.1 + xcmtouser} \
{rpn ..ylast.. yusertocm \
..fontsize.. pttocm 2 / -
ycmtouser}
set graylevel .draw_label_for_last_curve_graylevel.
delete .draw_label_for_last_curve_graylevel.
}
open file.dat
read columns x y
draw curve
\label = "Illustration"
Draw Label For Last Curve "\label"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
(Note that Gri has a built-in command
`<font color="#82140F"><code>draw label for last curve "\label"</code></font>' written much as above, so
there is no need for you to enter
this new command into your `<font color="#82140F"><samp>.grirc</samp></font>' file. But you might want to
check `<font color="#82140F"><samp>gri.cmd</samp></font>' to see how a full
command does checking of the calling syntax
(see <a href="InvokingGri.html#InvokingGri">Invoking Gri</a>).
<p>
</table>
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