Oh - I had missed that this one was problematic. Yes I agree this is a non-expert level query which should have clear semantics.
> On Jun 20, 2016, at 7:24 PM, Peter F. Patel-Schneider > <pfpschnei...@gmail.com> wrote: > > > SELECT ?x WHERE { ?x :p :b . > FILTER EXISTS { SELECT ?x WHERE { ?x :q :d . } } }