fcchcpABABAB...ABCABCABC
hcpfccABABAB...ABCABCABC
hcpfccABABAB...ABCABCABC
fcchcpABABAB...ABCABCABC
The tightest waytopack spheres:A-layerB-layerC-layerAsCstackingsequence(FCC)ABAstackingsequenceA-layerA-layer(HCP)R-layarA-layerB-layerA-layerABCABC...=fcc.ABAB...=hcp!