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+Explanation: You can ❰merge❱ the alternatives of a union using a record with one
+handler per alternative, like this:
+
+
+    ┌─────────────────────────────────────────────────────────────────────┐
+    │     let union    = < Left = +2 | Right : Bool >                     │
+    │ in  let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
+    │ in  merge handlers union : Bool                                     │
+    └─────────────────────────────────────────────────────────────────────┘
+
+
+... but the first argument to ❰merge❱ must be a record and not some other type.
+
+For example, the following expression is $_NOT valid:
+
+
+    ┌─────────────────────────────────────────┐
+    │ let handler = λ(x : Bool) → x           │
+    │ in  merge handler < Foo = True > : True │
+    └─────────────────────────────────────────┘
+                ⇧
+                Invalid: ❰handler❱ isn't a record
+
+
+You provided the following handler:
+
+↳ $txt0
+
+... which is not a record, but is actually a value of type:
+
+↳ $txt1
+
+Some common reasons why you might get this error:
+
+● You accidentally provide an empty record type instead of an empty record when
+  you ❰merge❱ an empty union:
+
+
+    ┌──────────────────────────────────────────┐
+    │ λ(x : <>) → λ(a : Type) → merge {} x : a │
+    └──────────────────────────────────────────┘
+                                      ⇧
+                                      This should be ❰{=}❱ instead