English: (A) Spherical capsids of various sizes are composed of 12 pentamers (represented as darkened pentagons) and a variable number of hexamers. (B) Quasi-equivalence [6] posits that one may produce a pentamer from a hexamer by removing one subunit and its environment (the shaded triangular region) and joining the unpaired interfaces. This operation imposes pentameric dihedral angle values (“endo angles”) onto its neighboring hexameric angles [11], which, if unchallenged, propagate through the hexamers (depicted by arrows) in what we call endo angle propagation.