num::unordered_set

Defined in header <core/types.hpp>

template <class K, class Hash = std::hash<K>, class Eq = std::equal_to<K>,
          class Alloc = std::allocator<K>>
using unordered_set = std::unordered_set<K, Hash, Eq, Alloc>;

std::unordered_set: a hash set with no key order, like Rust HashSet.