-------------------------
clojure.core/seq
([coll])
Returns a seq on the collection. If the collection is
empty, returns nil. (seq nil) returns nil. seq also works on
Strings, native Java arrays (of reference types) and any objects
that implement Iterable.
-------------------------
clojure.core/seq?
([x])
Return true if x implements ISeq
-----
Очевидно, пусто? основан на след. какая разница между пустыми? и ноль? Я так смущен.
clojure.core/empty?
([coll])
Returns true if coll has no items - same as (not (seq coll)).
Please use the idiom (seq x) rather than (not (empty? x))
И еще:
(not (seq? ())) ;;false
(not (seq ())) ;;true
(not nil) ;;true