Theory of Equivalence Relations (A, R) (E1) For all x : xRx. (E2) For all x, y : If xRy then yRx. (E3) For all x, y, z : If xRy and yRz then xRz. Logic in Computer Science – p.2/16
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
F= = F + “ = ” + 2 Axiom Schemata Axiom Schema 6 x = x. Axiom Schema 7 x = y ⊃ (SzxA ⊃ SzyA) where A is an atomic wff. A first order theory is a first-order theory with equality if it has a binary predicate = such that the wffs above are theorem of the theory
Interpretation over a singleton Let I be , and σ ∈ ΣI. 1. I(A)(σ) = I(∀xA)(σ). 2. I(t)(σ) = a. 3. I(Sx1,···,xn t1,···,tn A)(σ) = I(A)(σ). 4. I0(P), σ(P) ∈ {I(n), Ψ(n)} for every n-ary predicate constant (variable), where
