-1 4 setxrange
-2.5 2.5 setyrange

200 setwidth
200 setheight

/M {3 2} def
/M' {M OX axesympoint} def

[M M'] points

18 setfontsize
traceaxes
axesarrow

[M O M'] ligne

M projx O M 1 (<-) tripointarcarrow
M' O M projx 1.5 (->) tripointarcarrow

pointilles
[M projy M M' M' projy] ligne


setTimesItalic
   (O) O dltext
   (M) M urtext
   (M') M' drtext
   (a) M projx drtext
   (b) M projy ltext
   (-b) M' projy ltext
setSymbol
   (q) 1 .3 rtext
   (-q) 1.5 -.5 rtext