theorem Th106:
  L1 // L2 & L1 <> L2 implies ex P st L1 c= P & L2 c= P & P is being_plane
proof
  assume that
A1: L1 // L2 and
A2: L1 <> L2;
A3: L2 is being_line by A1,Th66;
  L1,L2 are_coplane & L1 is being_line by A1,Th66,Th97;
  hence thesis by A1,A2,A3,Th71,Th98;
end;
