join.md in alf-0.10.1

- old
+ new

@@ -7,12 +7,13 @@
 
 DESCRIPTION
 
 This operator computes the (natural) join of its operands. 
 
-Natural join means that, unlike what is commonly used in SQL, the join is 
-performed on common attribute names. You can use the `rename` operator if this 
-behavior does not fit your needs.
+Natural join means that, unlike what is commonly used in SQL, joining is based 
+on equality of all attributes that are shared between LEFT and RIGHT performed 
+on common attribute names. You can use the `rename` operator if this  behavior 
+does not fit your needs.
 
 When operands have no attribute in common, this operator naturally "degenerates" 
 to a cartesian product.
 
 EXAMPLE