{"id":"two-stack-queue-lazy-transfer","text":"`_transfer` only moves elements when `_out_stack` is empty — it never re-reverses elements already in `_out_stack`, which is the key invariant preserving both correctness and amortized cost.","truth_value":"IN","source":"entries/2026/06/06/implement-queue-using-stacks-solution.md","source_url":"","source_hash":"","justifications":[],"dependents":["two-stack-queue-amortized-via-lazy-transfer"],"metadata":{},"created_at":"","updated_at":"","reviewed_at":"","verified_at":"","retracted_at":"","explanation":{"steps":[{"node":"two-stack-queue-lazy-transfer","truth_value":"IN","reason":"premise"}]}}