Fixed the type of reduce in the docs.

doc/Control

@@ -94,7 +94,7 @@ pointwise : [ [a_11, a_12, ..., a_1n] |->| [a_21, a_22, ..., a_2n],
 
 map : (a |->| b) * |< [a] >| -> |< [b] >|
 
-reduce : ([a] |->| b) * |< [a] >| -> |< [c] >|
+reduce : ([a] |->| b) * ([b] |->| b) * |< [a] >| -> |< [c] >|
 
 
 Choice