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m{ (\w) \1 (?! \1) (\w) }x;
m{ (\w) \1 ... (?! \1 | \2) (\w) \3 \3 \3 \1 (?! \1 | \2 | \3) (\w) }x;
my $s = 'AABCCCCAD'; our $DEBUG = 1; ... warn "$s: $re\n" if $DEBUG; qr/$re/x; }