theorem
  M1 is Self_Reversible symmetric implies M1 is Orthogonal
proof
  assume
A1: M1 is Self_Reversible symmetric;
  then
A2: M1=M1@ by MATRIX_6:def 5;
  M1 is invertible & M1=M1~ by A1;
  hence thesis by A2,MATRIX_6:def 7;
end;
