Clairfy type object/instance .defined thing

Toss .defined and use better methods

doc/Language/classtut.pod6

@@ -104,8 +104,8 @@ through the C<has> keyword, and behaviors introduced through the C<method>
 keyword.
 
 X<|type object>
-X<|defined>
-X<|.defined>
+X<|DEFINITE>
+X<|.DEFINITE>
 
 Declaring a class creates a new I<type object> which, by default, is installed into
 the current package (just like a variable declared with C<our> scope).  This
@@ -115,16 +115,22 @@ classes. The example above uses the class name C<Task> so that other code can
 refer to it later, such as to create class instances by calling the C<new>
 method.
 
-Type objects are I<undefined>, in the sense that they return C<False> if you
-call the C<.defined> method on them. You can use this method to find out if
-a given object is a type object or not:
+You can use C<.DEFINITE> method to find out if what you have is an instance
+or a type object:
 
-    my $obj = Int;
-    if $obj.defined {
-        say "Ordinary, user-defined object";
-    } else {
-        say "Type object";
-    }
+    say Int.DEFINITE; # False (type object)
+    say 426.DEFINITE; # True  (instance)
+    
+    class Foo {};
+    say Foo.DEFINITE;     # False (type object)
+    say Foo.new.DEFINITE; # True  (instance)
+
+You can also use type smileys to only accept instances or type objects:
+
+    multi foo (Int:U) { "It's a type object!" }
+    multi foo (Int:D) { "It's an instance!"   }
+    say foo Int; # It's a type object!
+    say foo 42;  # It's an instance!
 
 =head1 State