| y0 + c ' + z = y + a ' + x, ∀ c, z, y1, a, x. y0 + c ' + z = y1 + a ' + x → a = c ∨ a ∈ z ∨ a ∈ y0, ∀ a0, y0, c, z, a, x. (a0 ' + y0) + c ' + z = y + a ' + x ∧ a0 ∈ y ∧ (∀ c, z, y1, a, x. y0 + c ' + z = y1 + a ' + x → a = c ∨ a ∈ z ∨ a ∈ y0) → a = a0 ∨ a = c ∨ a ∈ y0 ∨ a ∈ z ⊦ a = c, a = a0, a ∈ z, a ∈ y0 |
Used terms: c, z, y, a, x