reserve c,c1,c2 for Cardinal, G,G1,G2 for _Graph, v for Vertex of G;

theorem Th23:
  G.minDegree() = c & G.supDegree() = c implies G is c-regular
proof
  assume A1: G.minDegree() = c & G.supDegree() = c;
  let v;
  G.minDegree() c= v.degree() & v.degree() c= G.supDegree() by GLIB_013:35;
  hence v.degree() = c by A1, XBOOLE_0:def 10;
end;
