double-colon rules and multi-arch builds

[Robert P. J. Day]

  ok, i have a far more specific question about double-colon rules.
it has to do with their use in paul's multi-arch build recipe here:

http://make.paulandlesley.org/multi-arch.html#advanced

  part of that makefile are the rules:

 Makefile : ;
 %.mk :: ;

 % :: $(OBJDIR) ; :

and the question is simply, do either of those last two rules
*require* the double colon as opposed to a single colon?  i'm not
interested in issues of efficiency, just in absolute requirement.

rday