INCLUSION CRITERIA
An entry belongs in this subdivision if and only if it restricts weakening to secure a relevance or variable-sharing condition on implication, typically with a Routley-Meyer or related relational semantics.
Required: At least one of the following:
- A consequence relation enforcing variable sharing between antecedent and consequent
- A Routley-Meyer ternary-relation semantics or an equivalent relevant algebra
- An axiomatic relevant or entailment system (R, E, T, and relatives)
Not sufficient: Variable sharing imposed as a content condition without a substructural calculus (Hyperintensional). Dropping contraction alone (Affine) or exchange alone (Ordered). A linear calculus keyed to exact resource use rather than relevance (Linear).
Boundary: Relevance systems that are individuated primarily by many-valued or paraconsistent gap/glut semantics are cross-listed with Algebraic/Many-Valued. The substructural-logics hub connects to all Structural siblings.