Authority Research Note

COBOL ALTER Statement: Deterministic Guarantees Terminate

The COBOL ALTER statement modifies control flow targets at runtime. This makes the effective control-flow graph stateful and path-dependent. Deterministic guarantees derived from source artifacts terminate at this construct.

What this construct does

ALTER changes where a subsequent GO TO will proceed. The visible source code does not represent the effective runtime control flow once ALTER has executed.

Why provability terminates

Because the jump target depends on prior runtime state, a static analysis cannot prove which path is taken. A single program can exhibit different behavior under different execution histories without any source changes.

Governance consequence

When ALTER is present, a deterministic authority cannot assert migration equivalence. Proceeding requires elimination of ALTER or a separate proof model that changes the scope of what can be guaranteed.

Authority boundary statement

Where provability terminates, authority terminates.

Evidence and verification

Legacy Lens records the presence of ALTER, its location, and the bundle hash binding that evidence.
Legacy Lens does not infer which runtime target is taken.
Deterministic replay produces the same evidence with the same hash.

Verified authority record

View a verified bundle where ALTER is present: Download authority record (PDF)