Proving the Associativity of OR

Question

I need help proving the following:

(a ∨ b) ∨ c = a ∨ (b ∨ c)

I don't want the answer... just a hint that will help me understand the process of proving this.

Thank you.

Answer 1

Why not just prove it by doing all possible values of a , b and c = True , False ? -- there are only 2^3 = 8 different cases.

Here's a start, for a=T , b=F , c=T

(a v b) v c = a ∨ (b ∨ c)
(T v F) v T = T v (F v T)
      T v T = T v T
          T = T

(However, this isn't really a programming question...)

Answer 2

What is your axiom set?

Not knowing the set, you could build a truth table