80 setxunit
18 setfontsize
-1.2 3.5 setxrange
-1.2 3.5 setyrange

tracerepere
marks
pi ytick
pi 2 div ytick

/id { setxvar x } def

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

   /g {
Cos
   } def

pointilles
0 pi {g} Courbe

continu
2 setlinewidth
bleu

-0.99999 0.99999 {f} Courbe

noir

setTimesItalic 
   (Arccos)  -0.9 dup f urtext
   (cos)  2.8 dup g urtext
   (O) O drtext
setSymbol
    (p) 0 pi crtext
    (p/2) 0 pi 2 div urtext