| a ∈ z, ∀ y. (∀ a. a ∈ x0 ↔ a ∈ y) → # rmdup(x0) = # rmdup(y), ∀ a0. a0 ≠ a → (a0 ∈ x0 ↔ a0 ∈ y0 ∨ a0 ∈ z) ⊦ # rmdup(x0) + 1 = # rmdup(y0 + z), a ∈ y0, a ∈ x0 |
⊦ a ∈ x ↔ (∃ y, z. x = y + (a + z))
a ∈ rmdup(z) ↔ (∃ y, z0. rmdup(z) = y + (a + z0)), a ∈ z, ∀ y. (∀ a. a ∈ x0 ↔ a ∈ y) → # rmdup(x0) = # rmdup(y), ∀ a0. a0 ≠ a → (a0 ∈ x0 ↔ a0 ∈ y0 ∨ a0 ∈ z) ⊦ # rmdup(x0) + 1 = # rmdup(y0 + z), a ∈ y0, a ∈ x0
Used terms: a, rmdup(z)