fact: Definition assoc := hom / X 0 / X 1 / X 2 / X 3 IMP hom / X 0 / X 2 / X 4 / X 5 IMP hom / X 0 / X 4 / X 6 / X 7 IMP ((comp / X 0 / (comp / X 0 / X 7 / X 5) / X 3) EQU ((comp / X 0 / X 7 / (comp / X 0 / X 5 / X 3)))).