simplify2(end):-!.
simplify2(Exp+X):-
    write('Exp+X'),write(Exp),write('+'),write(X),nl,
    (  (retract(vv(X/N)),!,
        N1 is N+1,
        assert(vv(X/N1)))
    ;
        (   assert(vv(X/1)),write('@'))
    ),

    simplify2(Exp).
simplify2(X):-
    write('X'),write(X),nl,
    atomic(X),
    simplify2(end+X).


list_to_output([C/N|List],Sum,Out):-
    list_to_output(List,Sum1,Out1),
    (   atom(C),
        N>1,!,
        Out=Out1+C*N,
        Sum = Sum1
    ;   atom(C),!,
        Out=Out1+C,
        Sum = Sum1
    ;   integer(C),
        Sum is Sum1+(C*N),
        Out = Out1
    ).
list_to_output([],0,'').

simplify(Expression,Out1):-
    simplify2(Expression),
    findall(C/N,vv(C/N),List),
    list_to_output(List,Sum,Out),
    Out1 =Out+Sum.