diff --git a/src/util.h b/src/util.h
index 356ead8..8b869c6 100644
--- a/src/util.h
+++ b/src/util.h
@@ -287,46 +287,49 @@ class IntervalMap
 	void set_interval(K begin, K end, const V v) {
 		if (begin >= end) return;
 
-		// get interval that `begin` intersects with (inclusive)
-		iter begin_intersect = --my_map.upper_bound(begin);
-
-		// get interval that `end` intersects with (inclusive)
+		// get end intersector (inclusive)
 		iter end_intersect = --my_map.upper_bound(end);
 
-		// if required, insert at start
-		iter inserted_start = my_map.end();
-		if (begin_intersect->second != v) {
-			inserted_start = my_map.insert_or_assign(begin_intersect, begin, v);
-		}
-
 		// if required, insert at end
 		iter inserted_end = my_map.end();
 		if (end_intersect->second != v) {
 			inserted_end = my_map.insert_or_assign(end_intersect, end, end_intersect->second);
 		}
 
+		// get begin intersector (inclusive)
+		iter begin_intersect = --my_map.upper_bound(begin);
+
+		// if required, insert at start
+		iter inserted_start = my_map.end();
+		if (begin_intersect->second != v) {
+			inserted_start = my_map.insert_or_assign(begin_intersect, begin, v);
+		}
+
 		// delete everyone inside
 		iter del_start = inserted_start != my_map.end() ? inserted_start : begin_intersect;
-		if (del_start->first == begin) {
+		if (del_start->first < begin || (del_start->first == begin && std::prev(del_start)->second != v)) {
 			del_start++;
 		}
 
 		iter del_end = inserted_end != my_map.end() ? inserted_end : end_intersect;
+		if (del_end != my_map.end() && del_end->first == end && std::next(del_end) != my_map.end() && del_end->second == v) {
+			del_end++;
+		}
 
-		if (del_start != my_map.end()) {
+		if (del_start != my_map.end() && del_start->first < del_end->first) {
 			my_map.erase(del_start, del_end);
 		}
 	}
 
 	// iterator which traverses elements in sorted order (smallest to largest)
 	// O(1)
-	constexpr inline iter &begin() {
+	constexpr inline auto &begin() {
 		return my_map.begin();
 	}
 
 	// end of elements
 	// O(1)
-	constexpr inline iter &end() {
+	constexpr inline auto &end() {
 		return my_map.end();
 	}
 
@@ -338,7 +341,12 @@ class IntervalMap
 
 	// get value at key `k`
 	// O(log N)
-	const V operator[](K const& k) {
+	const inline V& operator[](K const& k) const {
+		return (--my_map.upper_bound(k))->second;
+	}
+	
+	// don't return reference because we don't want to allow map[whatever] = value as it would edit the next-earliest value instead of inserting a new element. (TODO: write better.)
+	inline V operator[](K const& k) {
 		return (--my_map.upper_bound(k))->second;
 	}
 
@@ -347,6 +355,18 @@ class IntervalMap
 		my_map.clear();
 		my_map.insert(my_map.end(), { std::numeric_limits<K>::lowest(), v });
 	}
+
+	// get num intervals overall
+	// always at least 1
+	constexpr int num_intervals() {
+		return my_map.size();
+	}
+
+	// get number of intervals in a range
+	// UNTESTED
+	constexpr int num_intervals(const K& start, const K& end) {
+		return get_interval(end) - get_interval(start);
+	}
 };
 
 #endif // __UTIL_H__