Array CodeRef sub truth for each elt[1] !grep { !$b->($_) } @$a
Any CodeRef scalar sub truth $b->($a)
- Hash Hash hash keys identical [sort keys %$a]~~[sort keys %$b]
+ Hash Hash hash keys identical (every key is found in both hashes)
Array Hash hash slice existence grep { exists $b->{$_} } @$a
Regex Hash hash key grep grep /$a/, keys %$b
undef Hash always false (undef can't be a key)