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Ruby version: ruby 1.9.0 (2004-05-10) [i686-linux]
The lcm method used by mathn (and defined in rational.rb)
is broken.
irb(main):001:0> require 'mathn'
true
irb(main):002:0> 4.lcm(6)
12
irb(main):003:0> 0.lcm(0)
ZeroDivisionError: divided by 0
from /usr/local/lib/ruby/1.9/rational.rb:319:in `div'
from /usr/local/lib/ruby/1.9/rational.rb:319:in `lcm'
from (irb):3
But the lcm of 0 and 0 is well-defined (and equal to 0).

Regards, Bret