## 7 Mathematical Expressions

Expressions share a common syntax each place they appear in PSPP
commands. Expressions are made up of *operands*, which can be
numbers, strings, or variable names, separated by *operators*.
There are five types of operators: grouping, arithmetic, logical,
relational, and functions.

Every operator takes one or more operands as input and yields exactly
one result as output. Depending on the operator, operands accept
strings or numbers as operands. With few exceptions, operands may be
full-fledged expressions in themselves.