code: public boolean remove(ExtendedPropositionDefinition def) {
          if (def instanceof TemporalExtendedPropositionDefinition) {
              if (removeAllRelations((TemporalExtendedPropositionDefinition) def)) {
                  return true;
              } else {
                  return false;
              }
          }
          boolean result = defs.remove(def);
          if (result) {
              recalculateChildren();
              this.defsAsListOutdated = true;
          }
          return result;
      }
docs: Removes an extended proposition definition, and all relations involving
  it.
  
  @param def
  an {@link ExtendedPropositionDefinition}.
  @return <code>true</code> if successful, <code>false</code>
  otherwise.