code: public Relation getRelation(TemporalExtendedPropositionDefinition lhsDef,
              TemporalExtendedPropositionDefinition rhsDef) {
          return this.defPairsMap.get(Arrays.asList(lhsDef, rhsDef));
      }
docs: Gets the relation between two temporal extended proposition definitions.
  
  @param lhsDef
  a {@link TemporalExtendedPropositionDefinition}.
  @param rhsDef
  a {@link TemporalExtendedPropositionDefinition}.
  @return a <code>Relation</code>, or <code>null</code> if none was
  found.