500 setheight
750 setwidth
-2 28 setxrange
-2 18 setyrange

26 0 stranslate
90 rotate

[1 1 .5 .5] {.4 setgray} Quadrillage

/A {1 2} def
/B {3 1} def

[A B] points
.8 setlinewidth
traceaxes
unites
[1 3] {xmark} apply
2 ymark

1.5 setlinewidth
[O A B] polygone

setTimesItalic
   (O) O dltext
   (A) A ultext
   (B) B urtext

<tex>
$$
   \vec \imath
$$
</tex>
.5 -.2 [2 dup] dctexlabel 
<tex>
$$
   \vec \jmath
$$
</tex>
-.2 0 [2 dup] ultexlabel