Ruby in Raku #2
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# Raku knows what you
# mean, even if you
# want to do math on
# an entire Array
my $cities = <London
Oslo
Paris
Amsterdam
Berlin>.Set;
my $visited = <Berlin Oslo>.Set;
say "I still need " ~
"to visit the " ~
"following cities: ",
($cities (-) $visited).keys
Raku
INFO