Desugared:
Test.f :: for all d, e. <Eq d> -> d -> d -> d -> [e]
Test.f =
    /\ t86 t91 -> \ dict.87 ->
	let dict.83 = dict.87 in
	let
	  f.78 =
	      \ x.61 y.62 z.63 ->
		  let
		    fail.92 =
			(error [t91])
			    "\"ds021.hs\", line 8: pattern-matching failure [function binding]\n"S
		  in 
		    case ((== t86) dict.83 x.61 y.62) of {
		      True -> Nil! t91
		      False ->
			  case ((/= t86) dict.87 x.61 z.63) of {
			    True -> Nil! t91
			    False -> Nil! t91
			  }
		    }
	in  f.78