recursion - Recursive list predicate in prolog -

i'm having difficulty assignment, have write 2 predicates:

remove_all/3 removes instances of given element out of list , output list without given variable, e.g.:

remove_all(a, [b,a,c,a,d], x)   

gives

x = [b,c,d]) 

and

remove_list/3 removes elements of given list out of list , outputs resulting list, e.g.:

remove_list([a,b], [b,a,c,a,d], x)   

gives

x=[c,d].   

this have:

remove_all(rema,[],[]). remove_all(rema,[rema|x],res) :-      remove_all(rema,x,res). remove_all(rema,[l|p],res) :-      remove_all(rema,p,nr), res=[l|nr].  remove_list([],listb, listres). remove_list([h|taila],listb,listres) :-      member(h,listb),      remove_all(h,listb,listres),     remove_list(taila,listres,listres) .  remove_list([s|tailb],listb,listres) :-      remove_list(tailb, listb, listres). 

now, remove_all works fine, not when use in remove_list predicate, remove instances of first element of list specifies element removed, example:

?- remove_list([1,2],[1,2,3,2,1],f). f = [2, 3, 2]  

it removes 1's.

anybody have idea do?