| a ∈ filter(x0, y), a ∈ y, ∀ y. filter(rmdup(x0), y) = rmdup(filter(x0, y)) ⊦ filter(rmdup(a ' + x0), y) = rmdup(filter(x0, y)) |
⊦ a ∈ filter(x, y) ↔ a ∈ x ∧ a ∈ y
a ∈ x0 ∧ a ∈ y, a ∈ y, ∀ y. filter(rmdup(x0), y) = rmdup(filter(x0, y)) ⊦ filter(rmdup(a ' + x0), y) = rmdup(filter(x0, y))
Used terms: y, x0, a