theorem Th12:
  for o be OperSymbol of MSSign U1 holds Den(o,MSAlg U1) = (the
  charact of U1).o
proof
  let o be OperSymbol of MSSign U1;
  MSAlg U1 = MSAlgebra(#MSSorts U1,MSCharact U1#) by MSUALG_1:def 11;
  hence Den(o,MSAlg U1) = ((MSCharact U1).o) by MSUALG_1:def 6
    .= ((the charact of U1).o) by MSUALG_1:def 10;
end;
