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the order of evaluation of the element descriptions in a set constructor are implementation-dependent. 

The evaluation of a factor consisting of a variable specifies an access to the variable and denotes the value of the variable; it is an error if the variable is undefined. 

The evaluation of a factor consisting of a function designator specifies an activation of the function that is denoted by the function identifier (see Section 10.3). Any actual parameters are substituted for their corresponding formal parameters (see Section 11.3). Upon completion of the activation's algorithm, the factor denotes the value of the result of the activation; it is an error if the result is undefined. 

## 8.2 Operators 

The rules of composition specify operator precedences according to four classes of operators. The operator not has the highest precedence, followed by the so-called mUltiplying operators, then the so-called adding operators, and finally, with the lowest precedence, the relational operators. Sequences of operators of the same precedence are executed from left to right. The rules of precedence are reflected in the EBNF rules for Expression, Simple-Expression, Term, and Factor (above). 

Operators are also classified as arithmetic, Boolean, set, and relational operators according to their operand and result types. 

8.2.1. Arithmetic operators. An arithmetic operator takes integer or real operands and yields an integer or real results. This table summarizes operators that take one operand (the signs). 

<img src='content_image/783588.jpg'>

This table summarizes the operators that take two operands. 

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