Can I check if all entities in a list have the same value for an attribute with a single query?

@grav you can look entities the do not have the same value as any other entity

[:find ?e :where [_ :attr ?v] (not-join [?e] [?e :attr ?v])]

@bahulneel: cool!

@grav this goes some way toward explaining http://math.stackexchange.com/questions/528990/relationship-between-universal-quantifier-and-existential-quantification-is-it

also, there's a mistake, the not-join should include ?v

also not sure the query is safe as there is a free variable in negated part that isn't in the positive part

@grav this would be better [:find (count-distinct ?v) :where [_ :attr ?v]]