function isRedundant(rawPrefix: string, rawSuffix: string): boolean {
  const prefix = _normalizedStops.get(rawPrefix);
  const suffix = _normalizedStops.get(rawSuffix);
  return _redundancies.get(prefix)?.has(suffix) === true;
}
Map all equivalencies to the normalized key for the stop category.  These
are the entries in the redundancy mapping