Nabla

set maxdepth 30

{ ry -90 } R1
{rx -90 } R1
{ x 30 y 30 z -3 s 90 90 1 h 90 } box

Rule R1 {
dbox
{ z 0.6 rx 5 } R1
}

Rule R1 {
dbox
{ z 0.6 rx -5 } R1
}

Rule R1 {
dbox
{ z 0.6 rz 5 } R1
}

Rule R1 {
dbox
{ z 0.6 rz -5 } R1
}

Rule R1 weight 0.01 {

}

Rule dbox {
{ s 1.5 1.6 0.5 } box
}

Rule dbox weight 0.5 {
{ ry 90 s 0.5 } R1
}

Rule dbox weight 0.5 {
{ rx 90 s 0.5 } R1
}