Occurrences on the superficial level
        	?- count(a,[a,b,c,[a,c],a],R).
        	R = 2
         	We can also generate a list with N identical elements
        	?- count(a,X,10).
        	X = [a,a,a,a,a,a,a,a,a,a]

         	count(_,[],0).
         	count(A,[A|L],N):- !,count(A,L,N1),N is N1+1.
         	count(A,[_|L],N):- count(A,L,N). 

	 	Occurrences of an atom in a list on all levels 
         	?- countt(a,[[[a],[c]],[c,a]],R).
         	R = 2
         	?- countt(a,[[[a],[b]],[c,a]],2).
         	true.
         	?- countt(X,[a,b,c,[a,b,c,[a]]],3).
         	X = a

         	countt(_,[],0).
         	countt(A,[A|L],N):- !,countt(A,L,N1),N is N1+1.
         	countt(A,[B|L],N):- atom(B),countt(A,L,N),!.
         	countt(A,[B|L],N):- countt(A,B,N1),countt(A,L,N2),N is N1+N2.