The HashSet policy class implements operations with the "hash table" data structure. This lets you associate an array of unique values with a user resource, add/remove elements to/from this array, and check whether the array associated with the resource contains the specified value.
A PSL description of the HashSet class is provided in the following file:
/opt/KasperskyOS-Community-Edition-<version>/toolchain/include/nk/hashmap.psl