// import settings; import graph;  // pdfviewer="evince"; // psviewer="evince";  // returns a pair representation of a relative number of the equivalent class pair pairRepresentation(int n){ 	if(n>0){ 		return(n,0); 	}else{ 		return(0,-n); 	} }  string nullString(real r){ 	return ""; }  void drawCoordinates(pair point, align align=NoAlign){ 	label("$("+string(point.x)+","+string(point.y)+")$",point,align); }  unitsize(50,50);  int num = 10; int i;  for (i=-1*num ; i<=num ; ++i) { 	pair point = pairRepresentation(i) ; 	dot(point,red);  	// equivalence classes labelled with usual names, in blue 	label("$\mathbf{"+string(i)+"}$",point,5SW,fontsize(17)+blue);  	int j; 	for(j=abs(i);j<num;++j) { 		drawCoordinates(point,E); 		pair nextpoint = point + (1,1);  		draw(point -- nextpoint,blue+Dotted+linewidth(2)); 		dot(point,red+linewidth(5));  		point=nextpoint; 	} 	dot(point,red); 	draw(point -- point+(0.5,0.5),blue+Dotted+linewidth(2)); 	dot(point,red+linewidth(5)); 	drawCoordinates(point,E); }  // axes  real decay=-0.2;  ticks tick=RightTicks(N=0,n=1,end=false,nullString); xaxis("$n_1$",YEquals(decay),decay,num+1.0,tick,Arrow); yaxis("$n_2$",XEquals(decay),decay,num+1.0,LeftTicks(N=0,n=1,end=false,nullString),Arrow);