theorem Th61:
  F is having_a_unity & F is associative & F is having_an_inverseOp implies
  (the_inverseOp_wrt F).(the_unity_wrt F) = the_unity_wrt F
proof
  assume that
A1: F is having_a_unity and
A2: F is associative & F is having_an_inverseOp;
  set e = the_unity_wrt F;
  F.(e,e) = e by A1,SETWISEO:15;
  hence thesis by A1,A2,Th60;
end;
