theorem Th46:
  for n being Nat holds G is n-Dregular implies G is 2*n-regular
proof
  let n be Nat;
  assume A1: G is n-Dregular;
  let v;
  thus v.degree() = v.inDegree() +` n by A1
    .= n+`n by A1
    .= 2*n;
end;
