Re: What about the name of the second prerequisite?

[積丹尼 Dan Jacobson]

OK, on (info "(make) Automatic Variables") has
after
'$<'
     The name of the first prerequisite.  If the target got its recipe
     from an implicit rule, this will be the first prerequisite added by
     the implicit rule (*note Implicit Rules::).
add:
     To get the name of the second etc. prerequisite, use e.g., $(word 2,$+).

Thanks Sam. We would have never guessed (that is was safe to recommend.)
(Maybe elaborate if it is safe to use other than $+ too.)