x0 + a ' = y0 + b ', ∀ x, a, b. x + a ' = y0 + b ' ∧ (a ∈ y0 ∨ a = b) ∧ (b ∈ x ∨ b = a) → x = y0 ∧ a = b, b = a0 ∨ b ∈ x0 ∨ b = a,
a = a0 ∨ a ∈ y0 ∨ a = b, a ∈ y0 ∨ a = b, b ∈ x0 ∨ b = a
⊦ x0 = y0 ∧ a = b
User applied rule all left
And closed the goal!
Rule argument
pos: left 2 terms: x0, a, b abort: F discard: F computed: T