import graph_pi;
size(200,0);
graphicrules(xmin=-1, xmax=4, ymin=-1, ymax=3);

grid(xstep=0,ystep=0);

cartesianaxis(xticks=Ticks(Label(Fill(white)), NoZero, ptick=invisible),
              yticks=Ticks(Label(Fill(white)), NoZero, ptick=invisible));

labelx("$O$",0,SW);

shipout(bbox(Fill(white)));