diff --git a/20.nix b/20.nix
new file mode 100644
index 0000000..599e961
--- /dev/null
+++ b/20.nix
@@ -0,0 +1,23 @@
+with import <nixpkgs> { };
+with stdenv.lib;
+let
+  list = [2 "4" true true {a = 27;} 2];
+  f = x: isString x;
+  s = "foobar";
+in
+{
+  #replace all X, everything should evaluate to true
+  ex00 = isList list;
+  ex01 = elemAt list 2 == true;
+  ex02 = length list == 6;
+  ex03 = last list == 2;
+  ex04 = filter f list == [ "4" ];
+  ex05 = head list == 2;
+  ex06 = tail list == [ "4" true true {a = 27;} 2 ];
+  ex07 = remove true list == [ 2 "4" {a = 27;} 2 ];
+  ex08 = toList s == [ "foobar" ];
+  ex09 = take 3 list == [ 2 "4" true ];
+  ex10 = drop 4 list == [ {a = 27;} 2 ];
+  ex11 = unique list == [ 2 "4" true {a = 27;} ];
+  ex12 = list ++ ["x" "y"] == [ 2 "4" true true {a = 27;} 2 "x" "y" ];
+}