{α : Type} →
  {P : Sort u} →
    {ref : IO.Ref α} →
      {mutex : Std.BaseMutex} →
        {ref' : IO.Ref α} →
          {mutex' : Std.BaseMutex} →
            { ref := ref, mutex := mutex } = { ref := ref', mutex := mutex' } → (ref ≍ ref' → mutex = mutex' → P) → P