Local rules are given for various virus capsid, or protein shell, geometries. Local rules specify local interaction patterns that can direct the self-assembly of coat and scaffolding subunits into different capsid geometries. They provide a mathematical abstraction allowing combinatorial anaylsis of possible assembly pathways. Local rules and simulations are provided for a geometry called "T = 7" such that a small change in the rules produces an alternate "T = 4" geometry. This is intriguing since evidence has been accumulating that some T = 7 capsids are closely related to T = 4 capsids.
