 #(even? (:val %))) ;; by function
=> #{{:id :3 :val 2}
     {:id :4 :val 2}}

(select o [:val 1])        ;; by shorthand value
=> #{{:id :1 :val 1}
     {:id :2 :val 1}}

(select o [:val even?])    ;; by shorthand function
=> #{{:id :3 :val 2}
     {:id :4 :val 2}}

(select o #{[:id :1]       ;; or selection
            [:val 2]})
=> #{{:id :1 :val 1}
     {:id :3 :val 2}
     {:id :4 :val 2}}

(select o [:id '((name)    ;; by shorthand expression
                 (bigint)
                 (odd?))])
=> #{{