reserve i,j,k,n,m for Nat,
  x,y,z,y1,y2 for object, X,Y,D for set,
  p,q for XFinSequence;
reserve k1,k2 for Nat;
reserve D for non empty set,
  F,G for XFinSequence of D,
  b for BinOp of D,
  d,d1,d2 for Element of D;
reserve F for XFinSequence,
        rF,rF1,rF2 for real-valued XFinSequence,
        r for Real,
        cF,cF1,cF2 for complex-valued XFinSequence,
        c,c1,c2 for Complex;

theorem
   Sum <%c1,c2%> = c1 + c2
proof
  c1 in COMPLEX & c2 in COMPLEX by XCMPLX_0:def 2;
  then addcomplex "**" <%c1,c2%> = addcomplex.(c1,c2) by Th38
     .= c1+c2 by BINOP_2:def 3;
  hence thesis;
end;
