size(5cm,5cm);

draw((-1,0)--(1,0),linewidth(1.2));
draw((0,0)--(0,4/3),dotted);
draw((-1/2,1)--(0,0),MidArrow);
draw((0,0)--(1/2,1),MidArrow);

int linespaces = 15;
for (int i = -linespaces-1; i < linespaces; ++i) {
    draw((i/linespaces,-.06)--((i+1)/linespaces,0));
}

label("$O$",(0,-0.02),S);
label("$A$",(-1,0),N);
label("$B$",(1,0),N);
label("$I$",(-1/2,1),NW);
label("$R$",(1/2,1),NE);
label("$N$",(0,4/3),N);