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ABAP Keyword Documentation → ABAP − Reference → Program Flow Logic → Expressions and Functions for Conditions → log_exp - Logical Expressions → rel_exp - Predicates →rel_exp - Predicate Functions
The return value of a predicate function is a logical value. A predicate function is a special formulation of a relational expression and, like any relational expression, can be a full logical expression or part of a logical expression. This means it can be specified as a condition in control statements, as an argument in Boolean functions, or in joins with Boolean operators.