-5 8 setxrange
-1 3 setyrange
20 setxunit

traceOx

xticks
0 xtick
[-1 1 3] {xmark} apply

1.7 setlinewidth
/D{7.7 -0} def   
/C{-4.7 -0} def 
gsave
0 4 translate
   orange
   [xmin -1] {0} apply
   (-]) ligne
   bleu
   [3 8] {0} apply
   ([-) ligne
grestore
rouge
   /arrowscale {2 dup} def
/angleA 60 def
/angleB 120 def
-1 0.5 1 0.5 (<-) pccurve


/angleA 60 def
/angleB 120 def
1 0.5 3 0.5 (->) pccurve
(2) 2 2.5 [2 dup] dctext
(2) 0 2.5 [2 dup] dctext

<tex>
$$
   +\infty
$$
</tex>

%% exemple 1 : simple
D dctexlabel 
<tex>
$$
   -\infty
$$
</tex>

%% exemple 1 : simple
C dctexlabel