unitsize(1cm);

pen p=invisible;
real marge=0.2, EspH=2, EspV=2;

object objet_1=draw("$R_n$",box,(EspH,EspV),marge,p),
       objet_2=draw("$\overline{R_n}$",box,(EspH,-EspV),marge,p),
       objet_11=draw("$A$",box,(2*EspH,EspV*3/2),marge,p),
       objet_12=draw("$\overline{A}$",box,(2*EspH,EspV*1/2),marge,p),
       objet_21=draw("$A$",box,(2*EspH,-EspV*1/2),marge,p),
       objet_22=draw("$\overline{A}$",box,(2*EspH,-EspV*3/2),marge,p),
       objet_111=draw("$B$",box,(3*EspH,EspV*11/6),marge,p),
       objet_112=draw("$\overline{B}$",box,(3*EspH,EspV*7/6),marge,p),
       objet_121=draw("$B$",box,(3*EspH,EspV*5/6),marge,p),
       objet_122=draw("$\overline{B}$",box,(3*EspH,EspV*1/6),marge,p),
       objet_211=draw("$B$",box,(3*EspH,-EspV*1/6),marge,p),
       objet_212=draw("$\overline{B}$",box,(3*EspH,-EspV*5/6),marge,p),
       objet_221=draw("$B$",box,(3*EspH,-EspV*7/6),marge,p),
       objet_222=draw("$\overline{B}$",box,(3*EspH,-EspV*11/6),marge,p);

add(new void(picture pic, transform t) {
    draw(pic,Label("$p_n$",UnFill(1)),(0,0)--point(objet_1,W,t),Center);
    draw(pic,Label("$q_n$",UnFill(1)),(0,0)--point(objet_2,W,t),Center);
    draw(pic,Label("$\frac{1}{20}$",UnFill(1)),point(objet_1,E,t)--point(objet_11,W,t),Center);
    draw(pic,Label("$\frac{19}{20}$",UnFill(1)),point(objet_1,E,t)--point(objet_12,W,t),Center);
    draw(pic,Label("$\frac{1}{5}$",UnFill(1)),point(objet_2,E,t)--point(objet_21,W,t),Center);
    draw(pic,Label("$\frac{4}{5}$",UnFill(1)),point(objet_2,E,t)--point(objet_22,W,t),Center);
    draw(pic,Label("$\frac{1}{20}$",UnFill(1)),point(objet_11,E,t)--point(objet_111,W,t),Center);
    draw(pic,Label("$\frac{19}{20}$",UnFill(1)),point(objet_11,E,t)--point(objet_112,W,t),Center);
    draw(pic,Label("$\frac{1}{5}$",UnFill(1)),point(objet_12,E,t)--point(objet_121,W,t),Center);
    draw(pic,Label("$\frac{4}{5}$",UnFill(1)),point(objet_12,E,t)--point(objet_122,W,t),Center);
    draw(pic,Label("$\frac{1}{20}$",UnFill(1)),point(objet_21,E,t)--point(objet_211,W,t),Center);
    draw(pic,Label("$\frac{19}{20}$",UnFill(1)),point(objet_21,E,t)--point(objet_212,W,t),Center);
    draw(pic,Label("$\frac{1}{5}$",UnFill(1)),point(objet_22,E,t)--point(objet_221,W,t),Center);
    draw(pic,Label("$\frac{4}{5}$",UnFill(1)),point(objet_22,E,t)--point(objet_222,W,t),Center);
});