Naming convention for symbols

For use in theory, it simplifies reading formulas when we stick to a general convention for naming variables of a particular type. Those naming conventions for symbols are summarized in the following table. For practical purpose, of course,  those naming conventions are non-rigid but arbitrary names are supported. Then the types are resolved by declaration.

Naming convention for symbols in theoretical settings
Level Kind of symbol Type constant variable
arity>0 arity=0 arity>0 arity=0
language Function symbol σ→τ f,g,h a,b,c   x,y,z
Predicate symbol (σ) p,q,r      
meta language Formula meta φ,ψ Φ,Ψ