code: <T extends Entity<?, ?>> Builder<BE, T> retreatTo(Relationships.WellKnown over, Class<T> entityType) {
          return new Builder<>(this, hop(), Query.filter(), entityType).hop(Related.asTargetBy(over), type(entityType));
      }
docs: Virtually identical to {@link #proceedTo(Relationships.WellKnown, Class)} only follows the relationship in the
  opposite direction.
  
  @param over       the relationship to retreat over (i.e. if the current position is the target of the
  relationship, the sought after entity type needs to be the source of the relationship).
  @param entityType the type of the entities to retreat to
  @param <T>        the type of the "target" entities
  @return a context builder with the modified source path, select candidates and type