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diff --git a/transfer/examples/aggregation/aggregate.tr b/transfer/examples/aggregation/aggregate.tr
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+import prelude
+import tree
+
+derive Eq Tree
+derive Compos Tree
+
+
+-- When the Transfer compiler gets meta variable inference,
+-- we can write:
+{-
+aggreg : (A : Type) -> Tree A -> Tree A
+aggreg _ t = 
+  case t of
+      ConjS c s1 s2 -> 
+	case (aggreg ? s1, aggreg ? s2) of
+		(Pred np1 vp1, Pred np2 vp2) | np1 == np2 -> 
+			Pred np1 (ConjVP c vp1 vp2)
+                (Pred np1 vp1, Pred np2 vp2) | vp1 == vp2 -> 
+	        	Pred (ConjNP c np1 np2) vp1
+		(s1',s2') -> ConjS c s1' s2'
+      _ -> composOp ? ? ? ? aggreg t
+-}
+
+-- Adding hidden arguments, we could write something like:
+{-
+aggreg : (A : Type) => Tree A -> Tree A
+aggreg t = 
+  case t of
+      ConjS c s1 s2 -> 
+	case (aggreg s1, aggreg s2) of
+		(Pred np1 vp1, Pred np2 vp2) | np1 == np2 -> 
+			Pred np1 (ConjVP c vp1 vp2)
+                (Pred np1 vp1, Pred np2 vp2) | vp1 == vp2 -> 
+	        	Pred (ConjNP c np1 np2) vp1
+		(s1',s2') -> ConjS c s1' s2'
+      _ -> composOp aggreg t
+-}
+
+
+-- For now, here's what we have to do:
+
+aggreg : (A : Type) -> Tree A -> Tree A
+aggreg _ t = 
+  case t of
+      ConjS c s1 s2 -> 
+	case (aggreg ? s1, aggreg ? s2) of
+		(Pred np1 vp1, Pred np2 vp2) | eq_NP np1 np2 -> 
+			Pred np1 (ConjVP c vp1 vp2)
+                (Pred np1 vp1, Pred np2 vp2) | eq_VP vp1 vp2 -> 
+	        	Pred (ConjNP c np1 np2) vp1
+		(s1',s2') -> ConjS c s1' s2'
+      _ -> composOp ? ? compos_Tree ? aggreg t
+
+
+-- aggreg specialized for Tree S
+aggregS : Tree S -> Tree S
+aggregS = aggreg S
+
+-- equality specialized for Tree NP
+eq_NP : Tree NP -> Tree NP -> Bool
+eq_NP = eq NP (eq_Tree NP)
+
+-- equality specialized for Tree VP
+eq_VP : Tree VP -> Tree VP -> Bool
+eq_VP = eq VP (eq_Tree VP)
+