| ∀ a. (x0 -l a) -l a = x0 -l a ⊦ ((a0 ' + x0) -l a) -l a = (a0 ' + x0) -l a |
a = a0, ∀ a. (x0 -l a) -l a = x0 -l a ⊦ ((a0 ' + x0) -l a) -l a = (a0 ' + x0) -l a
∀ a. (x0 -l a) -l a = x0 -l a ⊦ a = a0, ((a0 ' + x0) -l a) -l a = (a0 ' + x0) -l a
Used formulas: a = a0