-5 5 setxrange
-1 1 setyrange
20 setxunit

traceOx

xticks
0 xtick
[-2 0 1 3] {xmark} apply

1.7 setlinewidth

gsave
0 4 translate
   orange
   [xmin 0] {0} apply
   (-]) ligne
   bleu
   [1 3] {0} apply
   (]-[) ligne
grestore