-4 5 setxrange
-1 1 setyrange
20 setxunit

traceOx

xticks
0 xtick
[0 1] {xmark} apply

/A{-2 0} def   
/B {3 0} def
1.7 setlinewidth

[A B] ([-]) ligne

 setTimesItalic
   (a) A dltext
   (b) B drtext