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use warnings;
use strict;
...
    print "in=", pp @_;
    return lc $_[0]
}

say "lc: out=", pp( lc "A","B" );
print "mylc: "; say " out=", pp( mylc "A","B" );
...
# lc: out=("a", "B")
# mylc: in="A" out=("a", "B")
# mylc2: in=("A", "B") out="a"

my @x=qw/ X Y Z /;
say "lc: out=", pp( lc @x,"B" );
...
# lc: out=(3, "B")
# mylc: in=3 out=(3, "B")
# mylc2: in=("X", "Y", "Z", "B") out="x"

$_ = 'Z';
say "lc: out=", pp( lc,"B" );
...
# mylc: in="Z" out=("z", "B")
# Use of uninitialized value $_[0] in lc at example.pl line 12.
# mylc2: in=() out=("", "B")