import graph;
unitsize(1cm); 

real xmin=-4,xmax=4; 
real ymin=-4,ymax=4; 

real f(real x) {return log((3+x)/(3-x));}

marker cross=marker(scale(4)*rotate(45)*cross(4),1bp+red);
cross.mark(graph(f,-2.5,2.5,n=10)); 

draw(graph(f,-2.99,2.99,n=400),linewidth(1bp)); 

ylimits(-5,5,Crop); 
xaxis(Label("$x$",position=EndPoint, align=NE), 
      xmin=xmin,xmax=xmax, 
      Ticks(scale(.7)*Label(align=E), 
          NoZero, 
          begin=false,beginlabel=false, 
          end=false,endlabel=false, 
          Step=1,step=.25, 
          Size=1mm, size=.5mm, 
          pTick=black,ptick=gray), 
      Arrow); 
yaxis(Label("$y$",position=EndPoint, align=NE), 
      ymin=ymin,ymax=ymax, 
      Ticks(scale(.7)*Label(), 
          NoZero, 
          begin=false,beginlabel=false, 
          end=false,endlabel=false, 
          Step=1,step=.25, 
          Size=1mm, size=.5mm, 
          pTick=black,ptick=gray), 
      Arrow); 
real a=-2.95;
label("$f:x\mapsto\displaystyle\ln\left(\frac{3+x}{3-x}\right)$",(a,f(a)),E);