size(7.5cm);
transform Tx=shift(2.25,0), T;
for (int i=3; i <= 5; ++i) {
  draw(T*cross(i,round=false,r=0.5));
  draw(shift(0,-2.25)
       *T*cross(i+3,round=false,r=0.5));
  T *= Tx;
}