XOR of three values

Question

What is the simplest way to do a three-way exclusive OR?

In other words, I have three values, and I want a statement that evaluates to true IFF only one of

Answer 1

f= lambda{ |a| [false, false, true].permutation.to_a.uniq.include? a }
p f.call([false, true, false])
p f.call([false, true, true])

$ true

$ false

Because I can.