theorem Th98:
  for S being functional set, f be Function, i be set
     st f in S & i in dom product" S holds f.i in (product" S).i
proof
  let S being functional set, F be Function, i be set such that
A1: F in S;
  assume i in dom product" S;
   then (product" S).i = the set of all f.i where f is Element of S
      by A1,Th73;
 hence F.i in (product" S).i by A1;
end;
