1      Whenever you make a mistake while trying to invoke a "command", an error
 2 message is printed to tell you what went wrong.  If you misspell a command
 3 name, a message like the following will be printed:
 4 
 5 Segment such_and_so not found.
 6 
 7      If you make a mistake in the syntax of the "command line" or misspell the
 8 name of an "argument," you will get a message that is preceded by the
 9 name of the command you invoked.  For example, if you use the -directory
10 "control argument" with the print command, the following error message will be
11 printed:
12 
13 print:  Specified control argument is not accepted. -directory
14 
15      There are other types of error messages you may get, and they don't all
16 result from mistakes you make.  When you are unsure what a message means, the
17 best advice is to ask someone who does know.