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) :- strategic(X), strategic(Y).
non_strategic_pair(X,Y) :- company(X), company(Y), not strategic_pair(X,Y).

company(X1) :- produced_by(X,X1,X2,X3,X4).
company(X2) :- produced_by(X,X1,X2,X3,X4).
company(X3) :- produced_by(X,X1,X2,X3,X4).
company(X4) :- produced_by(X,X1,X2,X3,X4).
company(W) :- controlled_by(W,X1,X2,X3,X4).
company(X1) :- controlled_by(W,X1,X2,X3,X4).
company(X2) :- controlled_by(W,X1,X2,X3,X4).
company(X3) :- controlled_by(W,X1,X2,X3,X4).
company(X4) :- controlled_by(W,X1,X2,X3,X4).