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diff --git a/challenge-248/jo-37/perl/ch-2.pl b/challenge-248/jo-37/perl/ch-2.pl
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+++ b/challenge-248/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.24;
+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] [--] [M]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+M
+    a matrix in any format as accepted by the PDL string constructor,
+    e.g. '1,0,0;0,1,0;0,0,1'
+
+EOS
+
+
+### Input and Output
+
+say submatrix_sum("@ARGV");
+
+
+### Implementation
+
+sub submatrix_sum {
+	my $m = pdl @_;
+
+    $m->range(ndcoords($m(1:,1:)), 2)->reorder(2, 3, 0, 1)
+        ->clump(2)->sumover;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is submatrix_sum(
+            [1,  2,  3,  4],
+            [5,  6,  7,  8],
+            [9, 10, 11, 12])->unpdl,
+            [[14, 18, 22], [30, 34, 38]], 'example 1';
+
+        is submatrix_sum(
+            [1, 0, 0, 0],
+            [0, 1, 0, 0],
+            [0, 0, 1, 0],
+            [0, 0, 0, 1])->unpdl,
+            [[2, 1, 0], [1, 2, 1], [0, 1, 2]], 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+	}
+
+    done_testing;
+    exit;
+}