Proof of `Basic properties of Sprague–Grundy values` (2nd statement)
groundedproofs/Lax689614Proofs/Grundy.lean · lax-689614
What this proof establishes
Assuming the claims on the left, the claim on the right holds — checked by the archive's pipeline. Proof code is not displayed here.
Description
Backward induction: a winning move leads to value zero, and every positive value has such a move.