diff --git a/diff.js b/diff.js
index 9c2bfc3..40f8d2c 100644
--- a/diff.js
+++ b/diff.js
@@ -527,11 +527,17 @@ object.makeConstructor('IN', Object.assign(new LogicType(), {
 // XXX .key can't be a pattern at this point...
 // XXX this is a potential problem as with a pattern key we would need to
 // 		look ahead to pick the correct candidate...
+// XXX this falls into recursion on:
+// 		X = AT('moo')
+// 		X.value = OR(123, X)
+// 		cmp(X, {'moo', 333})
+// 			...this would also break on checking a recursive structure against 
+// 			a recursive pattern...
 var AT = 
 module.AT = 
 object.makeConstructor('AT', Object.assign(new LogicType(), {
 	__cmp__: function(obj, cmp){
-		if(cmp(obj[this.key], this.value)){
+		if(cmp(obj != null ? obj[this.key] : null, this.value)){
 			return true
 		}
 		return false
diff --git a/format.js b/format.js
index 4943426..eec7c34 100644
--- a/format.js
+++ b/format.js
@@ -52,7 +52,8 @@ var DIFF_FORMAT_FLAT =
 module.DIFF_FORMAT_FLAT = ARRAY(CHANGE) 
 
 
-// XXX
+// XXX it makes sense to make this a recursive pattern...
+// 		...need to check if we stop on a recursive pattern...
 var DIFF_FORMAT_TREE =
 module.DIFF_FORMAT_TREE = ANY