```utility functions
```
```diff --git a/src/islandairport/Utility.tl b/src/islandairport/Utility.tl
new file mode 100644
index 0000000..051f766
--- /dev/null
+++ b/src/islandairport/Utility.tl
```
```@@ -0,0 +1,35 @@
+package islandairport;
+
+import java.lang.Math;
+import java.awt.geom.Point2D;
+
+
+// calculates angle between two points
+// x1, y1 -> point a
+// x2, y2 -> point b
+public fun angleBetween(x1, y1, x2, y2) {
+    var dx = x2 - x2;
+    var dy = y2 - y1;
+    var angle = Math.atan2(dy, dx);
+    if (angle < 0)
+        return -angle;
+    return 2 * Math.PI - angle;
+}
+
+// Calculates the 2d distance between two points
+// x1, y1 point a
+// x2, y2 point b
+public fun distanceBetween(x1, y1, x2, y2) {
+    return Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2));
+}
+
+// tests whether a point is on the given line
+// px1, py1 -> the point to test
+// x2, y2, x3, y3 -> the line
+public fun onLine(px1, py1, x2, y2, x3, y3) {
+    var d23 = distanceBetween(x2, y2, x3, x3);
+    var d = distanceBetween(px1, py1, x3, y3) + distanceBetween(px1, py1, x2, y2);
+    var eps = 0.00000000001;
+
+    return (d + eps) > d23 && (d - eps) < d23;
+}
```