To express parallel computation explicitly, HPF defines the INDEPENDENT directive. It asserts that the statements in a particular section of code do not exhibit any sequentializing dependences; when properly used, it does not change the semantics of the construct, but may provide more information to the language processor to allow optimizations. A REDUCTION clause can be used with the INDEPENDENT directive to identify variables that are updated by commutative and associative operations. This facilitates the utilization of parallelism with reduction operations, in the context of loops where the order of accumulation of updates to a variable is insignificant.