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Comment by tromp | Hacker News Reader

> For Word, the condition 'r - l > 1' is true in all cases except when r=l.

Simplest counterexample: (l,r) = (0,1)

> For Word, the condition 'r - l > 1' is true in all cases where l>r.

Simplest counterexample: (l,r) = (1,0), although one should always have l <= r.

> Simplest counterexample: (l,r) = (1,0)

Then r-l is 0-1, which underflows.

  ghci> (0 :: Word) - (1 :: Word)
  18446744073709551615

> Then r-l is 0-1, which underflows.

True. Then (l,r) = (18446744073709551615,0) is a counterexample, since r-l = 1.

So is it not true that it is not true?

18446744073709551615 is greater than 1, isn't it?

Ah, of course, sorry!

> > For Word, the condition 'r - l > 1' is true in all cases except when r=l.

Was this a typo that 'moonchild fixed?

Yes.