add insurance functions example

archive/insurance_functions_example.md

@@ -0,0 +1,30 @@
+```python
+def find_subnets(nodes: list[Node]) -> list[tuple[Node, Node]]:
+    subnets = []
+    for i, (a, b) in enumerate(zip(nodes, nodes[1:])):
+        parent_node, dip = merge_two_nodes(a, b)
+        if parent_node == a or parent_node == b:
+            subnets.append((a, b))
+    return subnets
+
+
+def ensure_no_subnets(nodes: list[Node]):
+    if subnets := find_subnets(nodes):
+        raise Cidr4MergerError(f"There are subnets! {subnets=}")
+```
+
+
+```python
+def find_neighbors(nodes: list[Node]) -> list[tuple[Node, Node]]:
+    neighbors = []
+    for i, (a, b) in enumerate(zip(nodes, nodes[1:])):
+        parent_node, dip = merge_two_nodes(a, b)
+        if parent_node[1] + 1 == a[1] == b[1]:
+            neighbors.append((a, b))
+    return neighbors
+
+
+def ensure_no_neighbors(nodes: list[Node]):
+    if neighbors := find_neighbors(nodes):
+        raise Cidr4MergerError(f"There are neighbors! {neighbors=}")
+```