reserve FT for non empty RelStr;
reserve A for Subset of FT;
reserve T for non empty TopStruct;
reserve FMT for non empty FMT_Space_Str;
reserve x, y for Element of FMT;
reserve A, B, W, V for Subset of FMT;

theorem
  A^Fodelta = (A^Fob) /\ (A^Foi)`
proof
  ((A`)^Fob)`= A^Foi by Th37;
  hence thesis by Th39;
end;
