my_length(List, Length) :-
integer(Length) ->
Length >= 0,
my_make_list(Length, List)
;
my_length(List, 0, Length).
my_make_list(0, []):-
!.
my_make_list(N, [_| Tail]):-
M is N-1,
my_make_list(M, Tail).
my_length([], Length, Length).
my_length([_| Tail], Acc, Length) :-
Acc2 is Acc + 1,
my_length(Tail, Acc2, Length).
:- dynamic(pred_plain/0).
db_test_plain :-
repeat(100),
assertz(pred_plain),
fail.
retract(pred_plain),
db_test_plain.
