"simple".clj

; Integers and Longs are equal.
(= (Integer. 1) (Long. 1))
true

; Even negative ones.
(= (Integer. -1) (Long. -1))
true

; When you use them as keys in maps, the maps are still equal.
(= {(Integer. 1) :foo} {(Long. 1) :foo})
true

(= {(Integer. -1) :foo} {(Long. -1) :foo})
true

; When you use positive numbers as keys to sets, they're also equal.
(= #{(Integer. 1)} #{(Long. 1)})
true

; But negative ones aren't.  But only in sets.  Maps are fine.  lol.
(= #{(Integer. -1)} #{(Long. -1)})
false

hashing is hard.

Oh and just to laugh in my face:

#{(Integer. -1) (Long. -1)}

complains about a duplicate key. That little shitbag Mr. PersistentHashSet knows those keys are equal but won't let on when comparing.