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The example in the testcase introduced in D1667 currently fails with,

ClassOperator.hs:12:3: error:
    • Could not deduce (a ><> b0)
      from the context: a ><> b
        bound by the type signature for:
                   (**>) :: (a ><> b) => a -> a -> ()
        at ClassOperator.hs:12:3-44
      The type variable ‘b0’ is ambiguous
    • In the ambiguity check for ‘**>’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the class method:
        (**>) :: forall a b. (a ><> b) => a -> a -> ()
      In the class declaration for ‘><>’

ClassOperator.hs:12:3: error:
    • Could not deduce (a ><> b0)
      from the context: a ><> b
        bound by the type signature for:
                   (**<) :: (a ><> b) => a -> a -> ()
        at ClassOperator.hs:12:3-44
      The type variable ‘b0’ is ambiguous
    • In the ambiguity check for ‘**<’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the class method:
        (**<) :: forall a b. (a ><> b) => a -> a -> ()
      In the class declaration for ‘><>’

ClassOperator.hs:12:3: error:
    • Could not deduce (a ><> b0)
      from the context: a ><> b
        bound by the type signature for:
                   (>**) :: (a ><> b) => a -> a -> ()
        at ClassOperator.hs:12:3-44
      The type variable ‘b0’ is ambiguous
    • In the ambiguity check for ‘>**’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the class method:
        (>**) :: forall a b. (a ><> b) => a -> a -> ()
      In the class declaration for ‘><>’

ClassOperator.hs:12:3: error:
    • Could not deduce (a ><> b0)
      from the context: a ><> b
        bound by the type signature for:
                   (<**) :: (a ><> b) => a -> a -> ()
        at ClassOperator.hs:12:3-44
      The type variable ‘b0’ is ambiguous
    • In the ambiguity check for ‘<**’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the class method:
        (<**) :: forall a b. (a ><> b) => a -> a -> ()
      In the class declaration for ‘><>’

This is a regression relative to 7.10.2, which accepts the program without error.