The HELP command provides information about CIGAL commands, macros or
special topics. The most common usage for the HELP command is:
help subject
where 'subject' is the topic for which you want information. The nature
of the help information varies somewhat depending on the type of subject:

Internal Commands
If SUBJECT is an internal command, HELP prints out a description of
what the command does and how it is used. There is a HELP entry for
every CIGAL internal command. (Any unambiguous abbreviation can be
used for the command name.)
Macro Programs
If SUBJECT is the name of a macro program, HELP reads the macro
program and prints out any help information provided within the macro
(see below). If no help is present for a particular macro then the
HELP command prints nothing. It is up to the person who writes the
macro to include some help information with it.
Special Topics
SUBJECT can also be one of a variety of general topics available
that provides an overview to different aspects of using CIGAL.

All HELP information on 'internal commands' and 'special topics' is
stored in a special format in a single large disk file. The name of
this disk file is specified in CIGAL's string variable 'helpfile' (see
HELPFILE[4]). This filename is normally initialized automatically by the
start-up macro, SYSSTART. HELP information for 'macro programs' is
stored within the individual macros themselves (see below).

Rather than specifying each subject by name, you can also get HELP to
print information on any topic in the HELP file by simply specifying the
entry number as the first argument. Entries in the HELP file are stored
in alphabetical order by chapter, so that printing entries in order is a
useful way to print the entire manual.
(Note: When calling HELP entries by number the SUBJECT argument must be an
explicit number, or an expression that evaluates to a number. For
example, 'help 1' or 'help #1+#2' or 'help #1++' will work, but 'help #1'
will not because HELP will treat '#1' as a topic name.)

The HELP command and the MANUAL command are essentially identical
except that MANUAL prints a header at the top of each page. MANUAL is
recommended only when generating a printed manual.

Putting HELP into a macro:
Help information is entered into a macro program simply by including a
HELP command of the form:
help {
Enter whatever help messages you want to include.
The help message can contain as many lines as you wish.
}
anywhere within the macro. HELP commands of this form are ignored when
the macro is executed. However, when you ask for help for the macro, all
lines between the pair of brackets will be printed exactly as they
appear. (Note: MANUAL can not be used in place of HELP in this context.)

If HELP can find the specified entry it returns a value 0 in number
register 0 (#0); if it cannot find the entry it returns -1 in #0.

For more information, see INTRODUCTION[0], MANUAL[2], HELPFILE[4].