New lookup feature

[Olivier Gerard]

Good evening and happy new year to all members.

I like the new interface very much.
And the speed is really refreshing.

I would have a wish.

As one of the original purposes of the OEIS
was to find references for articles and books
dealing with a sequence, could we have a way to 
ask for entries with at least one published  REF ?

In the same spirit, at least one index entry, one
HTML Link, etc. ?

Currently   link:pdf    link:Sind   give a good
approximation of what I mean, but for the Ref field,
it is difficult to be generic.

Perhaps we could have an extension of the syntax
where Ref:  (without anything or with spaces after
the ':')  means  "check for at least one such non-empty line".

Olivier