theorem
  G is regular iff G.minDegree() = G.supDegree()
proof
  hereby
    assume G is regular;
    then consider c being Cardinal such that
      A1: G is c-regular;
    thus G.minDegree() = c by A1, Th22
      .= G.supDegree() by A1, Th22;
  end;
  assume G.minDegree() = G.supDegree();
  then G is G.minDegree()-regular by Th23;
  hence thesis;
end;
