Similar to 11, but with lists: explicit unification of lists can lead
to simplification.

-- a.cue --
x: [int, int, int] & [9, 8, 7]
-- out/trim-v3 --
== a.cue
x: [_, _, _] & [9, 8, 7]
-- diff/-out/trim-v3<==>+out/trim --
diff old new
--- old
+++ new
@@ -1,2 +1,2 @@
 == a.cue
-x: [int, int, int] & [9, 8, 7]
+x: [_, _, _] & [9, 8, 7]
-- out/trim-v3-noshare --
== a.cue
x: [_, _, _] & [9, 8, 7]
-- diff/-out/trim-v3-noshare<==>+out/trim --
diff old new
--- old
+++ new
@@ -1,2 +1,2 @@
 == a.cue
-x: [int, int, int] & [9, 8, 7]
+x: [_, _, _] & [9, 8, 7]
-- out/trim --
== a.cue
x: [int, int, int] & [9, 8, 7]
