
theorem Th52:
  for f being Function, x,y being object st [x,y] in LinTrace f holds
  {x} in dom f & y in f.{x}
proof
  let f be Function, x,y be object;
  assume [x,y] in LinTrace f;
  then [{x},y] in Trace f by Th50;
  hence thesis by Th31;
end;
