-- Syntax of FOL 
-- step (1) terms : constant, variabls, or succussive applications to functions. 
   -- examples of terms in number theory, set theory, min FOL 

-- step (2) atomic formulas : Relations over terms, = exists unless
specified.  
   -- examples of atomic formulas in number theory, set theory, min FOL 
-- step (3) wffs : atomic formulas, or formulas constructed from
smaller formulas using negation, implication, \forall, \exists.