theorem
  for x,L st (not x in L) & L is being_line holds ex L0 st x in L0 & L0
  // L & L0 <> L
proof
  let x,L;
  assume that
A1: not x in L and
A2: L is being_line;
  ex L0 st x in L0 & L0 // L by A2,Th72;
  hence thesis by A1;
end;
