-1 4 setxrange
-1 3 setyrange

200 setwidth
160 setheight
/M {3 2} def

18 setfontsize
traceaxes
axesarrow
unites

1 setlinewidth
O M (->) line
[O M] ligne
M point
pointilles
[M projy M M projx] ligne

setTimesItalic
   (O) O dltext
   (M) M urtext
   (a) M projx dctext
   (b) M projy bltext