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/* Comments /* can nest */ still a comment */ :- module(maplist, maplist/3) assert(world:done). % asserts sibling(X, Y) :- parent_child(Z, X), parent_child(Z, Y). parent_child(X, Y) :- father_child(X, Y). parent_child(X, Y) :- mother_child(X, Y). mother_child(trude, sally). father_child(tom, sally). father_child(tom, erica). father_child(mike, tom).