[S13] unspec multiple signatures

S06 is fairly stable at this point, and the suggestion in S13 to
support multiple signatures for one single routine never made it
into S06. Neither of three major implementations support multiple
signatures. There's no sense of a general demand for them. The
feature is probably implementable, but the torment to the
implementors isn't proportionate to the benefit for the users.

S13-overloading.pod

@@ -13,8 +13,8 @@ Synopsis 13: Overloading
 
     Created: 2 Nov 2004
 
-    Last Modified: 25 Oct 2010
-    Version: 15
+    Last Modified: 3 Nov 2011
+    Version: 16
 
 =head1 Overview
 
@@ -75,39 +75,10 @@ routine.  This can easily be handled with Perl 6's aliasing:
     &infix:<*> ::= &unimpl;
     &infix:</> ::= &unimpl;
 
-That's one solution, but often your alternatives all have the same
-name, and vary instead in their signature.  Some operators are
-commutative, or can otherwise take their arguments in more than
-one order.  Perl allows you to declare multiple signatures for a
-given body, and these will be pattern matched as if you had declared
-separate multi entries.  If you say:
-
-    multi sub infix:<+> (Us $us, Them $them) |
-                        (Them $them, Us $us) { myadd($us,$them) }
-
-that's equivalent to:
-
-    multi sub infix:<+> (Us $us, Them $them) { myadd($us,$them) }
-    multi sub infix:<+> (Them $them, Us $us) { myadd($us,$them) }
-
-except that there really is only one body.  If you declared a C<state>
-variable within the body, for instance, there would only be one
-of them.
-
 A C<multi> is in effect only within the scope in which it is defined or
 imported.  Generally you want to put your C<multi> subs into a package
 that will be imported wherever they are needed.
 
-When you use the multiple signature syntax, the alternate signatures
-are not required to all bind the same set of formal variable names,
-nor are all parameters of a given name required to bind with the
-same type.  Unbound parameters will be born with an undefined value
-(even if they have a default).  For any parameter that occurs in
-multiple signatures with non-identical nominal types, the actual
-lexical variable will declared with a nominal type of C<Mu>, and
-if unbound, will contain C<Mu>.  To catch parameter name typos,
-the compiler may warn about unused parameters.
-
 Conjectural: If the first parameter to a C<multi> signature is followed
 by an invocant colon, that signature represents two signatures, one
 for an ordinary method definition, and one for the corresponding C<multi>