-4 6 setyrange
%% -5 5 setxrange
quadrillage
.7 setlinewidth
tracerepere
marks
/f {
   1 sub dup mul 2 sub
}  def
/g {neg 1 add} def
/h {dup mul neg 3 add} def

1.5 setlinewidth
{f} courbe
{g} courbe
orange
{h} courbe