HP COBOL II Reference Manual

Conditional Expressions 

Conditional expressions identify conditions to be tested in order to
enable an object program to select alternate paths of control.  This
selection is determined by the truth value of a condition.  Conditional
expressions are used in the IF, SEARCH, EVALUATE and PERFORM statements.
There are two categories of conditions associated with conditional
expressions:  simple conditions and complex conditions.  You can enclose
either category within any number of paired parentheses without changing
its category.