theorem Th44:
  (a,b _|_ K implies K is being_line) &
  (K _|_ M implies K is being_line & M is being_line )
proof
  for a,b,K st a,b _|_ K holds K is being_line;
  then K _|_ M implies K is being_line & M is being_line;
  hence thesis;
end;
