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    1?- holdsAt(level(L),15/2).    2?- holdsAt(level(14),T).    3?- holdsAt(level(L),15/2).    4?- holdsAt(level(10/3),T).    5?- holdsAt(level(12),14).    6?- holdsAt(spilling,T).    7?- holdsAt(level(11),T).