drule must_be_emu(X): lle(X) => emu(X). drule must_be_ostrich(X): llo(X) => ostrich(X). fact not ( emu(X) and ostrich(X)). fact emu(X) => bird(X). fact ostrich(X) => bird(X). drule birdsfly(X): bird(X) => flies(X). drule birdsfeathered(X): bird(X) => feathered(X). drule emusdontfly(X): emu(X) => not flies(X). drule ostrichesdontfly(X): ostrich(X) => not flies(X). drule fliesoairborn(X): flies(X) => airborn(X).