Function map_to_canonical_relation 

pub fn map_to_canonical_relation(s: &str) -> String

Maps an arbitrary relation label to its canonical form, never producing a non-canonical value (GAP-SG-48).

Relation handling used to be inconsistent: non-canonical relations were accepted raw (with only a WARN) while non-canonical entity types were rejected outright. This unifies the policy — extraction never persists a label outside the canonical vocabulary. Known aliases are rewritten via a fixed table; values that are already canonical pass through unchanged; anything else falls back to the generic related.

Alias table (mirrors the project’s canonical relation map): adds/creates → causes, implements → supports, blocks → contradicts, tested_by → related, part_of → applies_to.