show difference between implicit and explicit state delcarator

doc/Language/variables.pod6

@@ -691,6 +691,14 @@ scope it should be copied to a new variable.
     foo() for ^3;
     # OUTPUT«one␤two␤three␤»
 
+Please note that the implicit state declarator is only applied to the variable
+itself, not the expression that may contain an initializator. If the
+initializer has to be called exactly once, the C<state> declarator has to be
+provided.
+
+    subset DynInt where $ = ::('Int'); # the initializer will be called for each type check
+    subset DynInt where state $ = ::('Int'); # the initializer is called once, this is a proper cache
+
 =head3 The C<@> Variable
 
 In a similar manner to the C<$> variable there is also a L<Positional>