30 setxunit
7.5 setborder
90 setangle_repere
-6 6 setxrange
-6 6 setyrange
/quadrillagegray 0.4 def
1 setquadrillagexstep
1 setquadrillageystep
quadrillage
1 1 settkstep
.5 .5 setsubtkstep
2 2 setmkstep
ticks
subticks
marks
traceaxes
axesarrow
unites
/f {setxvar
#rpn#   3*(x^2-1)/(1+x^2)
} def
gsave
   bleu
   .75 setlinewidth
   continu
   {f} courbe
grestore