60 setxunit
18 setfontsize
-3 3 setxrange
-3 3 setyrange

tracerepere
marks

/id { setxvar x } def

mixte
xmin xmax {id} Courbe
   /f {
Arctan
   } def

   /g {
      Tan
   } def

/h1 { setxvar pi 2 div } def
/h2 { setxvar 0 pi 2 div sub } def
/d1 {-1.57 -3 -1.57 3} def
/d2 {1.57 -3 1.57 3} def

continu
{h1} courbe
{h2} courbe
d1 droite
d2 droite

pointilles
   -1.57 1.57 {g} Courbe
   -1.57 pi add 1.57 pi add {g} Courbe
   -1.57 pi sub 1.57 pi sub {g} Courbe

continu
2 setlinewidth
bleu

 {f} courbe

noir

setTimesItalic 
   (Arctan)  2.2 dup f dctext
   (tan) 1.1 dup g ultext 
   (O) O drtext
setSymbol
    (p/2) 0 pi 2 div urtext
    (p/2)  pi 2 div 0 urtext