RESEARCH • POST‑INCIDENT • CITABLE

COBOL ALTER Statement Risk: Why Static Analysis Cannot Prove Control Flow

Authority posture: This research is cited inside authority records. It is not advice. It explains why authority terminates.

Post‑incident framing: this page defines a provability boundary that can terminate authority in regulated decisions. It is written to be cited inside authority records and to survive scrutiny.

Scope

This page explains what the boundary is, why deterministic guarantees collapse, and how authority records must describe termination without predicting outcomes for other systems.

What ALTER does

ALTER modifies the target of a GO TO at runtime. The program text may contain a fixed GO TO statement, but ALTER can change which paragraph will be executed when that GO TO is reached.

This makes the control-flow graph stateful. The next step depends not only on the current instruction pointer, but on which ALTER statements executed previously and in what order.

In practice, ALTER creates a runtime-mutable dispatch mechanism. It can be used deliberately (for state machines) or inherited as legacy technique. The key issue for provability is not intent. It is that the target is not statically fixed.

In practice, estates often combine multiple boundary classes. This page isolates one class so that authority language remains precise and citable.

Legacy Lens publishes precedent and invites comparison. It does not predict what will occur in other systems. The boundary definition is provided as a standard reference.

If an authority record cites this page, it should do so to define the evidentiary limit encountered in the analyzed corpus under the declared context.

Why static control-flow guarantees collapse

Static analysis can enumerate syntactic edges: where GO TO statements appear and which labels they reference. ALTER breaks that model because it rewrites those edges at runtime.

A proof claim requires that, given an input artifact set, the analyzer can determine the set of possible execution paths. With ALTER, the set of possible paths depends on execution history and runtime state.

Therefore, deterministic authority cannot assert global equivalence across transformations that might alter when or whether ALTER statements fire.

In practice, estates often combine multiple boundary classes. This page isolates one class so that authority language remains precise and citable.

Legacy Lens publishes precedent and invites comparison. It does not predict what will occur in other systems. The boundary definition is provided as a standard reference.

If an authority record cites this page, it should do so to define the evidentiary limit encountered in the analyzed corpus under the declared context.

Why testing does not restore provability

A test suite can exercise a subset of ALTER states. It cannot, in general, prove that other ALTER configurations are unreachable unless that unreachability is itself provable from artifacts.

In post-incident scrutiny, the question is whether an unobserved path could explain a discrepant outcome. If ALTER exists, a deterministic system must treat the possibility as open unless proven otherwise.

Legacy Lens therefore treats ALTER as an absolute provability boundary for authority issuance. It is not a judgment of defect. It is an evidentiary limit.

In practice, estates often combine multiple boundary classes. This page isolates one class so that authority language remains precise and citable.

Legacy Lens publishes precedent and invites comparison. It does not predict what will occur in other systems. The boundary definition is provided as a standard reference.

If an authority record cites this page, it should do so to define the evidentiary limit encountered in the analyzed corpus under the declared context.

Authority record language

Authority records should describe ALTER as a provability boundary: control-flow guarantees collapse; deterministic authority terminates at this construct.

They must avoid remediation guidance. They must avoid prediction. They must state only what occurred under the declared context for the analyzed corpus, and provide the file/line evidence anchors.

They should cite this research page as definitional context for why authority terminated.

In practice, estates often combine multiple boundary classes. This page isolates one class so that authority language remains precise and citable.

Legacy Lens publishes precedent and invites comparison. It does not predict what will occur in other systems. The boundary definition is provided as a standard reference.

If an authority record cites this page, it should do so to define the evidentiary limit encountered in the analyzed corpus under the declared context.

How to cite this research in an authority record

Use language such as:

This decision references Legacy Lens research (RESEARCH_COBOL_ALTER_RISK). The analysis explains a provability boundary where deterministic guarantees collapse. Where provability terminates, authority terminates under the declared governance context.

Explicit non‑claims