| ∀ z. rmdup(y0) \ z = rmdup(y0 \ z) ⊦ (a ∈ y0 ⊃ rmdup(y0);a ' + rmdup(y0)) \ z = rmdup((a ' + y0) \ z) |
a ∈ y0, ∀ z. rmdup(y0) \ z = rmdup(y0 \ z) ⊦ rmdup(y0) \ z = rmdup((a ' + y0) \ z)
∀ z. rmdup(y0) \ z = rmdup(y0 \ z) ⊦ (a ' + rmdup(y0)) \ z = rmdup((a ' + y0) \ z), a ∈ y0