Domains
	elem=symbol
	lis_elem=symbol*
Predicates
	member(elem,lis_elem)
Clauses
	member(X,[X|_]).
	member(X,[_|Y]):-member(X,Y).

    Source: geocities.com/v.iniestra/apuntes/pro_log

               ( geocities.com/v.iniestra/apuntes)                   ( geocities.com/v.iniestra)