\psset{unit=0.45cm}
%
\pspicture(-14,0)(10,15)
%\showgrid
% The labeled grid
\psset{linewidth=0.01,linecolor=gray}
\multido{\ny=0+1}{15}{
	\psline(-13,\ny)(10,\ny)
}
\multido{\nx=-13+1}{24}{
	\psline(\nx,0)(\nx,7)
}
\multido{\nx=-13+1}{24}{
	\psline(\nx,8)(\nx,14)
}
\multido{\ny=1+1}{13}{
	\rput(-14,\ny){$\scriptscriptstyle\ny$}
}
\setcounter{dummycount}{-12}
\multido{\nx=-12+1}{22}{
	\rput(\nx,-0.5){$\scriptscriptstyle\arabic{dummycount}$}
	\stepcounter{dummycount}
}
% Lines indicating the levels
%\psset{linewidth=0.3,linecolor=lightgray,fillstyle=none,linestyle=dashed,dash=7pt 4pt}
%\psline(-13,1)(9,1)
\psline(-13,7)(10,7)
%\psline(-13,13)(9,13)
% Labels
% Points r
\rput(-11.5,1.5){$\scriptstyle r_4$}
%\rput(-10.5,1.5){$\scriptstyle r_3$}
%\rput(-9.5,1.5){$\scriptstyle r_2$}
\rput(-8.5,1.5){$\scriptstyle r_1$}
%% Points s
\rput(-8.4,7.5){$\scriptstyle s_4$}
\rput(-6.4,7.5){$\scriptstyle s_3$}
\rput(-3.4,7.5){$\scriptstyle s_2$}
\rput(-0.4,7.5){$\scriptstyle s_1$}
%% Points t
%\rput(-0.5,13.5){$\scriptstyle t_4$}
\rput(2.5,13.5){$\scriptstyle t_3$}
%\rput(6.5,13.5){$\scriptstyle t_2$}
\rput(9.5,13.5){$\scriptstyle t_1$}
% The minimal point of intersection:
\pscircle[linewidth=0.15,linecolor=red,fillstyle=none](-4,9){0.55}
\rput(-3.35,9.65){$q$}
% Starting points
% Arcs at middle level
\psset{linewidth=0.1,linecolor=black,fillstyle=solid,fillcolor=white}
\psline[linewidth=0.5,linecolor=lightgray](-9,7)(-9,8)
\psline[linewidth=0.5,linecolor=lightgray](-7,7)(-7,8)
\psline[linewidth=0.5,linecolor=lightgray](-4,7)(-4,8)
\psline[linewidth=0.5,linecolor=lightgray](-1,7)(-1,8)
% Starting points at middle level
\pscircle(-9,7){0.3}
\pscircle(-7,7){0.3}
\pscircle(-4,7){0.3}
\pscircle(-1,7){0.3}
%
\pscircle(-9,8){0.3}
\pscircle(-7,8){0.3}
\pscircle(-4,8){0.3}
\pscircle(-1,8){0.3}
% The lattice paths
\psset{linewidth=0.15,fillstyle=none,linecolor=gray,linestyle=solid,linearc=0.3}
\psline(-9,1)(-6,1)(-6,3)(-4,3)(-4,9)(3,9)(3,10)(9,10)(9,13)
%\psline(-10,1)(-10,2)(-7,2)(-7,4)(-4,4)(-4,7)(-4,9)(1,9)(1,11)(6,11)(6,13)
%\psline(-11,1)(-11,5)(-7,5)(-7,7)(-5,7)(-5,11)(0,11)(0,12)(2,12)(2,13)
\psline(-12,1)(-12,7)(-7,7)(-7,9)(-4,9)(-4,11)(-3,11)(-3,13)(2,13)
% Starting points
\psset{linewidth=0.1,linecolor=black,fillstyle=solid,fillcolor=white}
% Starting points at lower level
\pscircle(-12,1){0.3}
%\pscircle(-11,1){0.3}
%\pscircle(-10,1){0.3}
\pscircle(-9,1){0.3}
% Starting points at upper level
%\pscircle(-1,13){0.3}
\pscircle(2,13){0.3}
%\pscircle(6,13){0.3}
\pscircle(9,13){0.3}
\endpspicture
