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($a & $b_mask) eq ($b & $a_mask)

  #    a   and mask[b]  eq      b   and mask[a]
  ($_[0][1] & $_[1][2]) eq ($_[1][1] & $_[0][2]);

Benchmark: timing 25000 iterations of cclever3, clever2, clever3, csim
+ple3, simple3...
  cclever3:  1 wallclock secs ( 0.95 usr +  0.00 sys =  0.95 CPU) 
...
             @ 24271.84/s (n=25000)
   simple3:  5 wallclock secs ( 3.97 usr +  0.01 sys =  3.98 CPU) 
             @ 6281.41/s (n=25000)

#!/usr/bin/perl

...
  }
  return 1;
}