Challenge 034 task 1

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diff --git a/challenge-034/jo-37/perl/ch-1.pl b/challenge-034/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use warnings FATAL => 'all';
+use Data::Dump qw(dd pp);
+use experimental qw(signatures postderef);
+die <<EOS unless @ARGV == 2;
+usage: $0 'A B C...' 'X Y Z...'
+
+'A B C...' 'X Y Z...'
+    two lists of words
+
+EOS
+
+
+### Input and Output
+
+main: {
+    # Split arguments.
+    my @a = split /\s+/, shift;
+    my @b = split /\s+/, shift;
+    # Create "sets" %a and %b having the elements of @a and @b as keys
+    # *and* values. Using hash slices to populate the hashes.
+    my %a;
+    @a{@a} = @a;
+    my %b;
+    @b{@b} = @b;
+    # Build the intersection of %a and %b by using the %a's keys to
+    # slice %b.
+    say join ' ', grep defined, @b{keys %a};
+}