theorem Th1:
   (SCM-VAL*SCM-OK).NAT = NAT
proof
   NAT in dom SCM-OK by Lm3,PARTFUN1:def 2;
   then
A1: (SCM-VAL*SCM-OK).NAT = SCM-VAL.(SCM-OK.NAT) by FUNCT_1:13;
   (SCM-VAL*SCM-OK).NAT = SCM-VAL.0 by A1,Def2,Lm3;
  hence thesis;
end;
