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Proof step 2 from proof firstN-lastN-in-01 (previous step)

a ∈ x, n < # x ⊦ x = [], a ∈ firstn(# x - n, x), a ∈ lastn(n, x)

User applied rule insert rewrite lemma

And obtained the following new goals

Rule argument

spec: list-del inst: name: firstN-lastN-in seq: ⊦ n ≤ # x ∧ a ∈ x ∧ ¬ a ∈ lastn(n, x) → (¬ a ∈ firstn(# x - n, x) ↔ false) subst: [n, x, a] → [n, x, a] flags: rewrite, current

Additional information

Used simplifier rules: lels-03: ⊦ m < n → m ≤ n; from specification nat Used terms: n, x, a