story: fix dif-ju correctness on empty input
:: ret = (~(int by a) uno) :: preserve only the entries whose keys are in a
::
::
- :: uno doesn't work if first argument is empty map
- ?: =(~ a) b
+ :: if 0 is the empty set,
+ :: a \ 0 = a
+ :: 0 \ b = 0 :: anything not in 0 but in b is by default 0
+ ?: =(~ a) ~
~& a
=/ uno=story
::~! ((~(uno by story-a) story-a) |=(* *proses))
