Why is UndecidableInstances not required here, for instance C1...

Why does GHC's type-checker accept this UndecidableInstance trick?...

Is it able to avoid UndecidableInstances in this example?...

GHC stuck due to UndecidableSuperClasses - expected behaviour or bug?...

Turing machine decidability ambiguous cases...

How can undecidable instances actually hang the compiler?...

Why does this code using UndecidableInstances compile, then generate a runtime infinite loop?...