// Remove from <by> elements, common with <Elements>,
// Create family <common> from common elements, with combined groups list.
// Remove from <by> elements, common with <Elements>,
// Create family <common> from common elements, with combined groups list.
bool IsEmpty () const { return myElements.empty(); }
// Check, if this family has empty list of elements
bool IsEmpty () const { return myElements.empty(); }
// Check, if this family has empty list of elements