theorem Th49:
  F is INT-valued implies Sum F = addint "**" F
proof
      assume A1:F is INT-valued;
  rng F c= COMPLEX by A1,MEMBERED:1;
  then A2:F is COMPLEX-valued by RELAT_1:def 19;
  per cases by NAT_1:14;
    suppose A3:len F=0;
      hence addint "**" F = 0 by Def8,A1,BINOP_2:4
                          .= Sum F by Def8,A2,A3,BINOP_2:1;
    end;
    suppose A4:len F>=1;
         A5: INT = INT /\ COMPLEX by MEMBERED:1,XBOOLE_1:28;
  now let x,y;assume x in INT & y in INT;
  then reconsider X=x,Y=y as Element of INT;
   addint.(x,y) = X+Y by BINOP_2:def 20;
   hence addint.(x,y) =addcomplex.(x,y) & addint.(x,y) in INT
     by BINOP_2:def 3, INT_1:def 2;
 end;
hence thesis by Th46,A4,A5,A1;
    end;
end;
