{0, 1}, i.e. define an evaluation e : Atoms → {0, 1}. Given an evaluation, we extend it to propositions using the truth tables: & : {0, 1} × {0, 1} → {0, 1} ⊃: {0, 1} × {0, 1} → {0, 1} A B A&B 0 0 0 0 1 0 1 0 0 1 1 1 A B A ⊃ B 0 0 1 0 1 1 1 0 0 1 1 1 If for all evaluations, a proposition takes the value 1 then we say it is always true (a tautology). 13