Type a backward-chaining rule and the goal-driven reading (Prolog).

Answer

playground_empty :- kids_not_outside. kids_not_outside :- playing_videogame. playing_videogame. ?- playground_empty.

Prolog reads each clause goal-driven: to prove playground_empty, prove kids_not_outside; to prove that, prove playing_videogame, which is a fact. The :- is "if", and the resolution + backtracking IS pattern_search — Prolog is the production system with unification as its matcher.