Clarity and correctness

Author: benjie

spec/Section 3 -- Type System.md

@@ -1707,13 +1707,18 @@ is constructed with the following rules:
 Further, if the input object is a _OneOf Input Object_, the following additional
 rules apply:
 
-- Prior to coercion of the input object literal, if the literal does not contain
-  exactly one entry, or if the value of this single entry is the {null} literal,
-  a _request error_ must be raised.
-
-- After coercion a the input object, if the resulting coerced unordered map does
-  not contain exactly one entry, or if this single entry has the value {null}, a
-  _request error_ must be raised.
+- Prior to the input object input coercion rules above:
+
+  - If the value of the input object is an input object literal and it does not
+    contain exactly one entry, or if the value of this single entry is the
+    {null} literal, a _request error_ must be raised.
+  - Otherwise, it must be a map supplied by a variable. If the map does not
+    contain exactly one entry, or if the value of this single entry is {null}, a
+    _request error_ must be raised.
+
+- After following the input coercion rules above, if the resulting coerced
+  unordered map does not contain exactly one entry, or if this single entry has
+  the value {null}, a _request error_ must be raised.
 
 Following are examples of input coercion for an input object type with a
 `String` field `a` and a required (non-null) `Int!` field `b`: