diff --git a/Canvas.cpp b/Canvas.cpp
index 793a1ef..4fe2876 100644
--- a/Canvas.cpp
+++ b/Canvas.cpp
@@ -53,6 +53,19 @@ bool Canvas::areHorizontalVertical(Point* p1, Point* p2, bool mode)
 		return HORIZ_pairs.count(makeOrderedPair<PointPair>(p1, p2));
 	else 
 		return VERT_pairs.count(makeOrderedPair<PointPair>(p1, p2));
+
+}
+
+bool Canvas::isLineHorizontal(Line* line)
+{
+	if (!line || !line->start_ref || !line->end_ref) return false;
+	return HORIZ_pairs.count(makeOrderedPair<PointPair>(line->start_ref, line->end_ref));
+}
+
+bool Canvas::isLineVertical(Line* line)
+{
+	if (!line || !line->start_ref || !line->end_ref) return false;
+	return VERT_pairs.count(makeOrderedPair<PointPair>(line->start_ref, line->end_ref));
 }
 
 bool Canvas::areAlreadyParallel(Line* l1, Line* l2)
@@ -60,6 +73,43 @@ bool Canvas::areAlreadyParallel(Line* l1, Line* l2)
 	return parallelPairs.count(makeOrderedPair<LinePair>(l1, l2));
 }
 
+void Canvas::remove_constraints()
+{
+	sys.clearByTag(constraints_count - 1);
+
+	switch (lastConstraint.mode) {
+	case Mode::Horizontal: {
+		if (auto* pair = std::get_if<PointPair>(&lastConstraint.data)) {
+			HORIZ_pairs.erase(*pair);
+		}
+		break;
+	}
+	case Mode::Vertical: {
+		if (auto* pair = std::get_if<PointPair>(&lastConstraint.data)) {
+			VERT_pairs.erase(*pair);
+		}
+		break;
+	}
+	case Mode::Parallel: {
+		if (auto* pair = std::get_if<LinePair>(&lastConstraint.data)) {
+			parallelPairs.erase(*pair);
+		}
+		break;
+	}
+	case Mode::Coincedent: {
+		if (auto* pair = std::get_if<PointPair>(&lastConstraint.data)) {
+			P2Ppairs.erase(*pair);
+		}
+		break;
+	}
+	default:
+		break;
+	}
+
+	lastConstraint.mode = Mode::None;
+	constraints_count--;
+}
+
 void Canvas::mousePressEvent(QMouseEvent* event)
 {
 	QPointF scene = event->pos();
@@ -92,18 +142,45 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 		Line* found = findAt(scene);
 
 		if (found) {
+			if (mode == Mode::Horizontal && isLineVertical(found)) {
+				QMessageBox::warning(this,
+					QString("Невозможно"),
+					QString("Эта линия уже вертикальна и не может быть горизонтальной!"),
+					QMessageBox::Ok
+				);
+				mode = Mode::None;
+				return;
+			}
+
+			// Проверка: если линия уже горизонтальна, нельзя сделать её вертикальной
+			if (mode == Mode::Vertical && isLineHorizontal(found)) {
+				QMessageBox::warning(this,
+					QString("Невозможно"),
+					QString("Эта линия уже горизонтальна и не может быть вертикальной!"),
+					QMessageBox::Ok
+				);
+				mode = Mode::None;
+				return;
+			}
+
 			if (mode == Mode::Horizontal) {
 				sys.addConstraintHorizontal(*found, constraints_count++);
-				HORIZ_pairs.insert(makeOrderedPair<PointPair>(found->start_ref, found->end_ref));
+				auto pair = makeOrderedPair<PointPair>(found->start_ref, found->end_ref);
+				HORIZ_pairs.insert(pair);
+				lastConstraint.mode = Mode::Horizontal;
+				lastConstraint.data = pair;
 			}
 			else {
 				sys.addConstraintVertical(*found, constraints_count++);
-				VERT_pairs.insert(makeOrderedPair<PointPair>(found->start_ref, found->end_ref));
+				auto pair = makeOrderedPair<PointPair>(found->start_ref, found->end_ref);
+				VERT_pairs.insert(pair);
+				lastConstraint.mode = Mode::Vertical;
+				lastConstraint.data = pair;
 			}
 			update();
+			after_constraint = true;
 		}
 		mode = Mode::None;
-		after_constraint = true;
 	}
 
 	else if (mode == Mode::DrawingLine) {
@@ -189,12 +266,16 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 		}
 
 		if (!areAlreadyParallel(found, current_line)) {
+			auto pair = makeOrderedPair<LinePair>(found, current_line);
 			sys.addConstraintParallel(*found, *current_line, constraints_count++);
-			parallelPairs.insert(makeOrderedPair<LinePair>(found, current_line));
+			parallelPairs.insert(pair);
+			lastConstraint.mode = Mode::Parallel;
+			lastConstraint.data = pair;
+
 			current_line = nullptr;
-			update();
 			mode = Mode::None;
 			after_constraint = true;
+			update();
 		}
 		else {
 			
@@ -251,7 +332,11 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 		}
 
 		sys.addConstraintP2PCoincident(*clickedPoint, *firstPoint, constraints_count++);
-		P2Ppairs.insert(makeOrderedPair<PointPair>(clickedPoint, firstPoint));
+		auto pair = makeOrderedPair<PointPair>(clickedPoint, firstPoint);
+		P2Ppairs.insert(pair);
+		lastConstraint.mode = Mode::Coincedent;
+		lastConstraint.data = pair;
+
 		firstPoint = nullptr;
 		mode = Mode::None;
 		after_constraint = true;
@@ -338,8 +423,7 @@ void Canvas::paintEvent(QPaintEvent*)
 		}
 		else if (res == SolveStatus::Failed && after_constraint){
 			QMessageBox::warning(this, QString("Error!"), QString("Last constraint is unavailable!"));
-			sys.removeConstraint(sys.get_last_constraint());
-			constraints_count--;
+			remove_constraints();
 		}
 		after_constraint = false;
 	}
@@ -388,7 +472,6 @@ Canvas::Canvas(QWidget *parent)
 	: QWidget(parent)
 {
 	sys = System();
-	current_line = nullptr;
 	setMouseTracking(true);
 	setBackgroundRole(QPalette::Base);
 	setAutoFillBackground(true);
@@ -396,19 +479,26 @@ Canvas::Canvas(QWidget *parent)
 
 Canvas::~Canvas()
 {
-	for (Line* line : lines) {
-		delete line;
-	}
-
 	for (double* param : params) {
 		delete param;
 	}
 
-	lines.clear();
+	for (Point* pt : points) {
+		delete pt;
+	}
+
+	for (Line* line : lines) {
+		delete line;
+	}
+
 	params.clear();
 	points.clear();
+	lines.clear();
+
 	parallelPairs.clear();
 	P2Ppairs.clear();
+	VERT_pairs.clear();
+	HORIZ_pairs.clear();
 
 	if (current_line) 
 		delete current_line;
diff --git a/Canvas.h b/Canvas.h
index c129e6a..ec40cd3 100644
--- a/Canvas.h
+++ b/Canvas.h
@@ -54,6 +54,8 @@ private:
     Point* findPointAt(QPointF, qreal tolerance = 5.0);
     bool areCoincident(Point*, Point*);
     bool areHorizontalVertical(Point*, Point*, bool);
+    bool isLineHorizontal(Line* line);           // проверяет, горизонтальна ли линия
+    bool isLineVertical(Line* line);             // проверяет, вертикальна ли линия
     // ====================== Параллельность ======================
     bool areAlreadyParallel(Line* l1, Line* l2);           // проверка на дубликат
 
@@ -62,6 +64,8 @@ private:
     Line* draggedLine{ nullptr };
     QPointF dragOffset;
 
+    // ====================== Работа с парами ограничений ======================
+    void remove_constraints();
     // ====================== Данные сцены ======================
     System               sys;                     // геометрический солвер
     QVector<Line*>       lines;                   // завершённые линии
@@ -80,4 +84,10 @@ private:
 
     int obj_count{ 0 };            // тег для новых объектов
     int constraints_count{ 0 };   // тег для новых ограничений
+
+    struct LastConstraint {
+        Mode mode{ Mode::None };
+        std::variant<LinePair, PointPair> data;
+    };
+    LastConstraint lastConstraint;
 };
\ No newline at end of file