I quickly came up with at least two:

  DB<1> x 0 && qw(t r u e) || qw(f a l s e)
0  'f'
1  'a'
2  'l'
3  's'
4  'e'
  DB<2> x 1 && qw(t r u e) || qw(f a l s e)
0  'e'
# Oops!
  DB<3> x 1 && 2 || "two"
0  2
  DB<4> x 1 && 0 || "two"
0  'two'
# Oops!
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So "b" can't be a false value and can't be a list.

        - tye (but my friends call me "Tye")