a solution with O(NlogN) cost and with low memory consumption:

use strict;
use warnings;

my $data = do { local $/; lc <DATA> };
my @words = $data =~ /\w+/g;

{
    no warnings;

    sub cmpix {
        for (my $off = 0;; $off++) {
            my $cmp = $words[$a+$off] cmp $words[$b+$off];
            return $cmp if $cmp;
        }
    }
}

my @ixs = sort cmpix 0..$#words;

# replace this code with duplication detector (it
# should be easy!):
for my $ix (@ixs) {
    print substr(join(" ", @words[$ix..$#words]), 0, 50), "\n";
}


__DATA__
...
[download]

that outputs...

$ perl ./t.pl
1519
2nd may 1519
a character in the discworld series of novels is b
at clos luc france on 2nd may 1519
based largely on leonardo da vinci leonardo da vin
character in the discworld series of novels is bas
clos luc france on 2nd may 1519
da vinci died at clos luc france on 2nd may 1519
da vinci leonardo da vinci died at clos luc france
died at clos luc france on 2nd may 1519
discworld series of novels is based largely on leo
france on 2nd may 1519
in the discworld series of novels is based largely
is based largely on leonardo da vinci leonardo da
largely on leonardo da vinci leonardo da vinci die
leonard of quirm a character in the discworld seri
leonardo da vinci died at clos luc france on 2nd m
leonardo da vinci leonardo da vinci died at clos l
luc france on 2nd may 1519
may 1519
novels is based largely on leonardo da vinci leona
of novels is based largely on leonardo da vinci le
of quirm a character in the discworld series of no
on 2nd may 1519
on leonardo da vinci leonardo da vinci died at clo
quirm a character in the discworld series of novel
series of novels is based largely on leonardo da v
the discworld series of novels is based largely on
vinci died at clos luc france on 2nd may 1519
vinci leonardo da vinci died at clos luc france on
[download]

then finding duplicates is pretty obvious as they appear in consecutive entries in @ixs.

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