strategic(X1) | strategic(X2) | strategic(X3) | strategic(X4) :- produced_by(X,X1,X2,X3,X4). strategic(W) :- controlled_by(W,X1,X2,X3,X4), strategic(X1), strategic(X2), strategic(X3), strategic(X4). :- strategic_pair(X,Y), not strategic(X). :- strategic_pair(X,Y), not strategic(Y).