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Proof step 7 from proof blastN-len (previous step)

# x = n0 + n, ∀ x0, n0, n. # x0 < # x → # x0 = n0 + n → # butlastn(n, x0) = n0 ⊦ # butlastn(n, x) = n0, x = []

User applied rule insert spec-lemma

And obtained the following new goals

Proof step 8:
⊦ x ≠ [] → (∃ y, a. x = y + a ')
Proof step 9:
# x = n0 + n, x ≠ [] → (∃ y, a. x = y + a '), ∀ x0, n0, n. # x0 < # x → # x0 = n0 + n → # butlastn(n, x0) = n0 ⊦ # butlastn(n, x) = n0, x = []

Rule argument

spec: list name: lastdiv seq: ⊦ x ≠ [] → (∃ y, a. x = y + a ') subst: [x] → [x]

Additional information

Used terms: x