Interpretation An interpretation I of F is , where D is a non-empty set called the domain of individuals. I0 is a mapping defined on the constants of F satisfying 1. If c is an individual constant, then I0(c) ∈ D. 2. If f n is an n-ary function constant, then I0(f n) : Dn → D
Axiom Schemata for F Axiom Schema 1 A ∨ A ⊃ A Axiom Schema 2 A ⊃ (B ∨ A) Axiom Schema 3 A ⊃ B ⊃ (C ∨ A ⊃ (B ∨ C)) Axiom Schema 4 ∀xA ⊃ Sxt A where t is a term free for the individual variable x in A Axiom Schema 5 ∀x(A ∨ B) ⊃ (A ∨ ∀xB) provided that x is not free in A