Fix typo

Author: ax0

book/src/merklestatements.md

@@ -9,7 +9,7 @@ all of which are represented as `MerkleTree` on the back end.
 
 The frontend compound types and their implementation as Merkle trees is explained under [POD value types](./values.md#dictionary-array-set).  The backend structure of a MerkleTree is explained on [the Merkle tree page](./merkletree.md).
 
-The POD2 interface provides statements for working with Merkle trees and compond types at all layers of the stack:
+The POD2 interface provides statements for working with Merkle trees and compound types at all layers of the stack:
 - Primitive statements for Merkle trees
 - General derived statements for Merkle trees
 - Specialized `ContainsKey`, `NotContainsKey`, and `ContainsValue` statements for the three front-end types.