-3 6 setxrange
quadrillage

.7 setlinewidth
tracerepere
marks

/f {
   setxvar
   2 x mul
   x dup mul sub
   3 add
} def

1.3 setlinewidth
{f} courbe

16 setfontsize
setTimesItalic
   (C) -1.5 dup f (-5 0) ultext
   (f) indice