COMPONENTS:
nominal sets semantics
(if atoms are urelemente, what do unknowns correspond to? Jamie has an answer
 if atoms are urelemente, does their instantiations mean? Jamie has an answer)
freshness 
treatment of alpha-equivalence using permutations
dendence or levels of variables
atoms are also data in the sense that there names matter and may be compared on syntactical distinctness (inidentity)

atoms were designed to model abstract syntax trees.