Perhaps this is -too- idiomatic, but for recipe 04-08 (You want to find elements in one array but not in another):

Though if when is considered a statement modifier in this case, and if you can't combine statement modifiers in p6 (much as you cannot in p5), then that likely doesn't work. In that case:

For numeric @a, and $_ will these be equivalent:

( $_ == none( @a ) ) && say "foo";
( $_ ~~ none( @a ) ) && say "foo";
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