light_source{-9 rgb 2}#macro P()pigment{#end#macro D()#declare#end D()C=P()rgb z}D()E=P()rgb x}D()J=0;#macro Q(U,V)P()checker P()U translate.5}P()V}scale.5}#end#while(J<4)D()B=Q(C,E)D()C=Q(C,B)D()E=Q(E,B)D()J=J+1;#end plane{z,3 P()B}}