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Proof step 17 from proof int2bytes-first-neg (previous step)

int2bytes(i1 / 256) + int2bytes((i1 + 255) % 256).last ' = by ' + bytes, 0 ≤ b2i(by), i1 < ~383, i1 < 0, ∀ bytes, by, i0. i→n(i0) < i→n(i1 + 255) → int2bytes(i0) = by ' + bytes ∧ by ∈ int2bytes(i0) ∧ 0 ≤ b2i(by) ∧ i0 < 0 → false ⊦ ¬ by ∈ int2bytes(i1 / 256) ∧ by ≠ int2bytes((i1 + 255) % 256).last, int2bytes((i1 + 255) % 256).last ≠ by ∧ ¬ int2bytes((i1 + 255) % 256).last ∈ bytes

User applied rule insert rewrite lemma

And obtained the following new goals

Proof step 18:
bytes ≠ [] ⊦ bytes0 + by ' = bytes ↔ bytes0 = bytes.butlast ∧ by = bytes.last
Proof step 19:
by ' + bytes ≠ [], int2bytes(i1 / 256) = (by ' + bytes).butlast ∧ int2bytes((i1 + 255) % 256).last = (by ' + bytes).last, 0 ≤ b2i(by), i1 < ~383, i1 < 0, ∀ bytes, by, i0. i→n(i0) < i→n(i1 + 255) → int2bytes(i0) = by ' + bytes ∧ by ∈ int2bytes(i0) ∧ 0 ≤ b2i(by) ∧ i0 < 0 → false ⊦ ¬ by ∈ int2bytes(i1 / 256) ∧ by ≠ int2bytes((i1 + 255) % 256).last, int2bytes((i1 + 255) % 256).last ≠ by ∧ ¬ int2bytes((i1 + 255) % 256).last ∈ bytes

Rule argument

seq: bytes ≠ [] ⊦ bytes0 + by ' = bytes ↔ bytes0 = bytes.butlast ∧ by = bytes.last subst: [bytes, by, bytes0] → [by ' + bytes, int2bytes((i1 + 255) % 256).last, int2bytes(i1 / 256)] rotate: F spec: list-last inst: bytelist name: splitlasteq

Additional information

Used simplifier rules: ⊦ ¬ bytes + bytes0 ≠ [] ↔ bytes = [] ∧ bytes0 = [];% ⊦ by ' ≠ [];% ⊦ (bytes + bytes0) + bytes1 = bytes + bytes0 + bytes1; Used terms: by ' + bytes, int2bytes((i1 + 255) % 256).last, int2bytes(i1 / 256)