14:17 >perl 958_SoPW.pl
Histogram 1:  { a => 2, b => 5, c => 7 }
Histogram 2:  { b => 3, c => 1, d => 4 }
Union:        { a => 2, b => 8, c => 8, d => 4 }
Intersection: { b => 3, c => 1 }
XOR:          { a => 2, d => 4 }

14:17 >