diff --git a/libs/main/containers/piset.h b/libs/main/containers/piset.h
index 6453703a..6eb413dd 100644
--- a/libs/main/containers/piset.h
+++ b/libs/main/containers/piset.h
@@ -181,6 +181,10 @@ public:
 		return *this;
 	}
 
+	//! \~english Tests if element `key` exists in the set.
+	//! \~russian Проверяет наличие элемента `key` в массиве.
+	inline bool contains(const T & t) const { return _CSet::contains(t); }
+
 	//! Returns if element "t" exists in this set
 	bool operator[](const T & t) const { return _CSet::contains(t); }
 
@@ -192,25 +196,21 @@ public:
 
 	//! Unite set with "v"
 	PISet<T> & unite(const PISet<T> & v) {
-		for (typename PIMap<T, uchar>::const_iterator i = v.begin(); i != v.end(); ++i)
-			_CSet::insert(i.key(), 0);
+		for (const auto & i: v)
+			_CSet::insert(i, 0);
 		return *this;
 	}
 
 	//! Subtract set with "v"
 	PISet<T> & subtract(const PISet<T> & v) {
-		for (typename PIMap<T, uchar>::const_iterator i = v.begin(); i != v.end(); ++i)
-			_CSet::remove(i.key());
+		for (const auto & i: v)
+			_CSet::remove(i);
 		return *this;
 	}
 
 	//! Intersect set with "v"
 	PISet<T> & intersect(const PISet<T> & v) {
-		for (typename _CSet::iterator i = _CSet::begin(); i != _CSet::end(); ++i)
-			if (!v.contains(i.key())) {
-				_CSet::remove(i.key());
-				--i;
-			}
+		_CSet::removeWhere([&v](const T & k, uchar) { return v.contains(k); });
 		return *this;
 	}
 
@@ -229,16 +229,16 @@ public:
 	//! Returns content of set as PIVector
 	PIVector<T> toVector() const {
 		PIVector<T> ret;
-		for (typename _CSet::const_iterator i = _CSet::begin(); i != _CSet::end(); ++i)
-			ret << i.key();
+		for (const auto & i: *this)
+			ret << i;
 		return ret;
 	}
 
 	//! Returns content of set as PIDeque
 	PIDeque<T> toDeque() const {
 		PIDeque<T> ret;
-		for (typename _CSet::const_iterator i = _CSet::begin(); i != _CSet::end(); ++i)
-			ret << i.key();
+		for (const auto & i: *this)
+			ret << i;
 		return ret;
 	}
 };