%% code obsolete, desole...
-6 6 setxrange
-1 2 setyrange

300 setheight
375 setwidth

/I {.5 1} def

/f {
   setxvar
   x 2 exp 2 x * + 1 +
   x 2 exp 2 +
   div
} def
/f' {
   setxvar
   x 2 exp neg x + 2 + 2 mul
   x 2 exp 2 + 2 exp
   div
} def

/g {pop 1} def

tracerepere
marks
.5 ymark
1.5 ymark

tracecourbe

gsave
   mixte 
   tracegcourbe
grestore

2 dup f dashpoint
I point

1.6 settailletangente
-1 tracetangente
2 tracetangente

4 settailletangente
0 tracetangente

setTimesItalic
   (C) .95 xmax mul dup f uplefttext
   (f) indice
   (T) -1.2 -.7 uplefttext
   (I) I downrighttext

setSymbol
   (D) .95 xmax mul 1 downlefttext