|  |  D.15.9.3 member Procedure from librarycombinat.lib(see  combinat_lib).
 
Example:Usage:
member(e,L); e def, L list
 
Return:
1 if e is an element of L, 0 otherwise
Theory:
we require the elements involved to have a compare operator ==.
 |  | LIB "combinat.lib";
member(1,list(1,4,5));
==> 1
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