async
a(1, 2, 3).
d(A, B, C) :- a(A, B, C).
b(C, B, A) :- d(A, B, C).
b(3, 2, 1)?
----
----
b(3, 2, 1) -> d(1, 2, 3) -> a(1, 2, 3)
----
---- (no newline)