theorem :: SPRECT_3:26
  LSeg(NE-corner P,SE-corner P) c= L~SpStSeq P
proof
A1: LSeg(NW-corner P,NE-corner P) \/ LSeg(NE-corner P,SE-corner P) c= (LSeg(
NW-corner P,NE-corner P) \/ LSeg(NE-corner P,SE-corner P)) \/ (LSeg(SE-corner P
  ,SW-corner P) \/ LSeg(SW-corner P,NW-corner P)) by XBOOLE_1:7;
  LSeg(NE-corner P,SE-corner P) c= (LSeg(NW-corner P,NE-corner P) \/ LSeg(
  NE-corner P,SE-corner P)) by XBOOLE_1:7;
  then
  LSeg(NE-corner P,SE-corner P) c= (LSeg(NW-corner P,NE-corner P) \/ LSeg(
NE-corner P,SE-corner P)) \/ (LSeg(SE-corner P,SW-corner P) \/ LSeg(SW-corner P
  ,NW-corner P)) by A1;
  hence thesis by SPRECT_1:41;
end;
