-4.5 4.5 setxrange
-4 3 setyrange

/A {4 1} def
/B {4 -2} def
/C {-4 -2} def
/D {-4 3} def


A C droite
B D droite

/O {A C B D interdroite} def

B O A .5 (=) tripointarc
D O C .5 (=) tripointarc
 
O point

setTimesItalic
   (x) A ultext
   (y) B urtext
   (x') C drtext
   (y') D dltext
   (O) O dctext