Most ordinary letters are accepted as variables. These may be subscripted or superscripted so long as it is understood that the variable formed is not semantically compound. For example "x_i" can be used for "x-inner" if no reference to a variable "i" is intended. For most mathematical purposes these variables are all that is needed.

Symbolic logic expressions and some definitions require some special kinds of variables shown here:
\pvar - \tvar Sentential Variables
\ppvar -\ttvar More Sentential Variables
\pbar - \rbar Unary Predicate Variables
\pbarp - \rbarp Binary Predicate Variables
\pbarpp - \rbarpp Ternary Predicate Variables
\ubar - \wbar Unary Function Symbol Variables
\ubarp - \wbarp Binary Function Symbol Variables
\ubarpp - \wbarpp Ternary Function Symbol Variables


(\pvar \Iff \qvar \c (\pvar \c \qvar))

(x = y \c \pbar x \Iff \pbar y)

(x \in \setof t \pbar t \Iff \pbar x \and x \in \U)