SYSML21 — Guard check binds a Boolean to an Expression variable

TransitionFeatureMembership::validateTransitionFeatureMembershipGuardExpression: Guard check binds a Boolean to an Expression variable

Where:          SysML 2.0 (formal/2026-03-02), §8.3.18.8 TransitionFeatureMembership, PDF p.372 (printed 340)
Published OCL:  kind = TransitionFeatureKind::guard implies transitionFeature.oclIsKindOf(Expression) and let guard : Expression = transitionFeature.oclIsKindOf(Expression) in guard.result.specializesFromLibrary('ScalarValues::Boolean') and guard.result.multiplicity <> null and guard.result.multiplicity.hasBounds(1,1)
Correction proposed: kind = TransitionFeatureKind::guard implies transitionFeature.oclIsKindOf(Expression) and let guard : Expression = transitionFeature.oclAsType(Expression) in guard.result.specializesFromLibrary('ScalarValues::Boolean') and guard.result.multiplicities()->exists(m | m.allSupertypes()->including(m)->selectByKind(MultiplicityRange)->exists(r | r.hasBounds(1, 1)))
Proof of fault: (a) A Boolean is bound to a variable declared Expression and then navigated as one. (b) Guard results never own a multiplicity, so the rule refuses every guard the library allows.
Likely cause:   Original authoring error (no similar rule). No rule in KerML or SysML is similar (best match 25%): a wrong operator (test instead of cast), plus a multiplicity test that the library never satisfies.
Basis of fix:   (a) is determined (the cast). (b) is an interpretation: owned-or-inherited multiplicity.