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Proof step 2 from proof lastn-neq (previous step)

lastn(n, x) = a ' + y, n ≤ # x ⊦ a ∈ x

Heuristic simplifier applied rule simplifier

And closed the goal!

Rule argument

Additional information

Used simplifier rules: lastN-in-01: ⊦ ¬ a ∈ x ∧ n ≤ # x → ¬ a ∈ lastn(n, x);%a: ⊦ (x + y) + z = x + y + z; from specification list%in-14: ⊦ a ' + x = y → a ∈ y; (forward) from specification list