Prerequisites

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• Check that your issue is not already filed:
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• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
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Description

In the following example

class A

class B extends A where
  b : Unit

class C extends A, B

instance : A where

instance : B where
  b := ()

instance : C where

The last line produces an error fields missing: 'b'. If, instead, I change the order of the inherited classes of C, as such

class C extends B, A

then it works.

Versions

Tried both on my computer (Lean 4.12.0 on NixOS/nixpkgs unstable) and on live.lean-lang.org.

Impact

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