Well looky there... you know, it never occurred to me to put an empty list into a list with map to skip an entry. I was thinking in terms of Lisp, where adding '() gives you a nil entry. I assumed the result would have been to add 0 or something, even though I knew

map {  ( 0..$_ ) } ( 1..3 );
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yields

(0, 1, 0, 1, 2, 0, 1, 2, 3)
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Cool.