diff --git a/fsharp/ygosim/src/Utils.fs b/fsharp/ygosim/src/Utils.fs
index dbf2036..74c8dff 100644
--- a/fsharp/ygosim/src/Utils.fs
+++ b/fsharp/ygosim/src/Utils.fs
@@ -9,6 +9,9 @@ module List =
 
     let (.->) = setIndex
 
+    let toIndices list = List.mapi (fun i _ -> i) list
+    let containsIndex index list = index >= 0 && index < List.length list
+
 module Lens =
     open FSharpPlus.Lens