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Proof step 27 from proof nodups-butlastn (previous step)

a ∈ a0 ' + butlastn(n, x), n ≤ 1 + # x, n ≤ # x, ∀ a, n. a ∈ butlastn(n, x) ∧ n ≤ # x → a ∈ x ⊦ a = a0, a ∈ x

Heuristic simplifier applied rule simplifier

And obtained the following new goals

Proof step 28:
a ∈ butlastn(n, x), n ≤ # x, n ≤ 1 + # x, ∀ a, n. a ∈ butlastn(n, x) ∧ n ≤ # x → a ∈ x ⊦ a = a0, a ∈ x

Rule argument

Additional information

Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ a ≠ b → (a ∈ b ' + x ↔ a ∈ x); (s)