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diff --git a/challenge-207/jo-37/perl/ch-2.pl b/challenge-207/jo-37/perl/ch-2.pl
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+++ b/challenge-207/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0 '!float';
+use PDL;
+use PDL::NiceSlice;
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [N...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N...
+    calculate the H-Index for the given numbers
+
+EOS
+
+
+### Input and Output
+
+say hirsch(@ARGV);
+
+
+### Implementation
+
+sub hirsch {
+    # Compare the reverse-sorted list's elements with their index
+    # position and pick the largest index where the difference is
+    # positive.  Finally adjust the zero-based array index to the
+    # one-based H-Index.
+    which(pdl(@_)->qsort->(-1:0) > sequence(scalar @_))->((-1)) + 1;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is hirsch(10, 8, 5, 4, 3), 4, 'example 1';
+        is hirsch(25, 8, 5, 3, 3), 3, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is hirsch(9, 7, 6, 2, 1), 3, 'from Wikipedia';
+        is hirsch(1, 7, 6, 2, 9), 3, 'same, not sorted';
+        is hirsch(5, 5, 5, 5, 5), 5, 'last index';
+	}
+
+    done_testing;
+    exit;
+}