procedure xturn(t:integer);
    begin
      course:=course+t;
      if course > 4 then course:=course-4;
    end;

  procedure forwrd(f:integer);
    var i:integer;
    begin
      case course of
        1:y:=y+f*ysize;
        2:x:=x+2*f*xsize;
        3:y:=y-f*ysize;
        4:x:=x-2*f*xsize;
      end;
      moveto(x,y);
    end;

  procedure jump(j:integer);
    begin
      case course of
        1:y:=y+j*ysize;
        2:x:=x+2*j*xsize;
        3:y:=y-j*ysize;
        4:x:=x-2*xsize;
      end;
      grxx1:=x;
      grxy1:=y;
    end;

  procedure hilbert(A,XSIZE,YSIZE:INTEGER);
    begin
      case flag of
        1:begin
            if a=0 then xturn(3)
                   else begin
                          a:=a-1;
                          flag:=2;
                          hilbert(A,XSIZE,YSIZE);
                          forwrd(2);
                          xturn(3);
                          flag:=1;
                          hilbert(A,XSIZE,YSIZE);
                          xturn(1);
                          forwrd(2);
                          flag:=1;
                          hilbert(A,XSIZE,YSIZE);
                          forwrd(2);
                          xturn(3);
                          flag:=2;
                          hilbert(A,XSIZE,YSIZE);
                          a:=a+1;
                        end;
         end;
        2:begin
            if a=0 then xturn(1)
                   else begin
                          a:=a-1;
                          flag:=1;
                          hilbert(A,XSIZE,YSIZE);
                          xturn(1);
                          forwrd(2);
                          flag:=2;
                          hilbert(A,XSIZE,YSIZE);
                          forwrd(2);
                          xturn(3);
                          flag:=2;
                          hilbert(A,XSIZE,YSIZE);
                          xturn(1);
                          forwrd(2);
                          flag:=1;
                          hilbert(A,XSIZE,YSIZE);
                          a:=a+1
                        end
          end
       end
    end;