use strict;
use warnings;

sub recursiveFringe {
  for( @{ +shift } ) {
    if( ref $_ ) { recursiveFringe( $_ ) } else { print "$_\n" };
  }
}

sub sameFringe {
  # create a subthread for each tree executing the above recursiveFringe
  # in such a way that the output from print above can be read in
  # while(<...>) in the main thread.
  # once a difference occurs return FALSE and terminate threads
}

my @trees = (
             [ [ 1, [ [2, [4, 7] ], 5 ] ], [3, [6, [8, 9] ] ] ],
             [ [ 1, [ [2, [4, 7] ], 5 ] ], [3, [6, [8, 9] ] ] ],
             [ [ 1, [ [ [2, 4], 7], 5 ] ], [3, [6, [8, 9] ] ] ],
             [ [ 1, [ [2, [4, 7] ], 5 ] ], [3, [6, [8, [9, 0 ] ] ] ] ],
             [ [ 1, [ [0, [4, 7] ], 5 ] ], [3, [6, [8, 9] ] ] ],
);
print sameFringe( $trees[0], $_ )?"Same\n":"Different\n" for @trees;