+Note [Multiple instantiation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
+For example, consider
+ f :: forall a. Eq a => forall b. Ord b => a -> b
+At a call to f, at say [Int, Bool], it's tempting to translate the call to
+
+ f_m1
+ where
+ f_m1 :: forall b. Ord b => Int -> b
+ f_m1 = f Int dEqInt
+
+ f_m2 :: Int -> Bool
+ f_m2 = f_m1 Bool dOrdBool
+
+But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
+a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
+ f_m1 = f_mx
+But it's entirely possible that f_m2 will continue to float out, because it
+mentions no type variables. Result, f_m1 isn't in scope.
+
+Here's a concrete example that does this (test tc200):
+
+ class C a where
+ f :: Eq b => b -> a -> Int
+ baz :: Eq a => Int -> a -> Int
+
+ instance C Int where
+ baz = f
+
+Current solution: only do the "method sharing" thing for the first type/dict
+application, not for the iterated ones. A horribly subtle point.
+
+