theorem Th20:
  for G being unital non empty multMagma
  for M1,M2 being well-unital strict MonoidalExtension of G
    holds M1 = M2
proof
  let G be unital non empty multMagma;
  let M1,M2 be well-unital strict MonoidalExtension of G;
A1: un(M1) = the_unity_wrt op(M1) & un(M2) = the_unity_wrt op(M2) by Th17;
  the multMagma of M1 = the multMagma of G & the multMagma of M2 = the
  multMagma of G by Def22;
  hence thesis by A1;
end;
