Basic explanation of 59692

message-index/messages/GHC-59692/index.md

@@ -0,0 +1,12 @@
+---
+title: Duplicate instance declarations
+summary: An instance has been defined twice for the same type.
+introduced: 9.6.1
+severity: error
+---
+
+You can only define a single instance for every type, because it must be possible to automatically resolve class constraints without any ambiguity.
+
+Note that instances are considered the same even if they have different constraints. Only the arguments of the class are considered when matching instances.
+
+See the [GHC User Guide](https://downloads.haskell.org/~ghc/9.10.1/docs/users_guide/exts/instances.html) for more information on instance declarations and resolution.