Numeric variables created with IF are initially set to the system-missing value. By
default, they are assigned an F8.2 format.
Logical expressions are evaluated in the following
order: functions, followed by exponentiation, arithmetic operations,
relations, and logical operators. When more than one logical operator
is used, NOT is evaluated first,
followed by AND, and then OR. You can change the order of operations
using parentheses.
Assignment expressions are evaluated in the following
order: functions, then exponentiation, and then arithmetic operators.