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

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

The primitive symbols of E are those of F, plus the symbol ∃. The formation Rules of E are those of F, plus the following If B is a wff of E and x is an individual variable, then ∃xB is a wff of E. The axiom schemata of E are those of F plus

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

The need for a richer language In P, it is not possible to express assertions about elements of a structure. First Order Logic is a considerably richer logic than propositional logic, but yet enjoys many nice mathematical properties

Substitutivity of Equivalence Let A,M and N be wffs and let AMN be the result of replacing M by N at zero or more occurrences (henceforth called designate occurrences) of M in A. 1. AMN is a wff. 2. If |= M ≡ N then |= A ≡ AMN

Some Properties 1. ∆n is consistent. 2. Γ ⊆ ∆n ⊆ ∆n+1 ⊆ ∆Γ 3. ∆Γ is complete. 4. If ∆Γ ` A then there exists n ∈ N such that ∆n ` A. 5. A ∈ ∆Γ iff ∆Γ ` A 6. ∆Γ is consistent

Syntax Formation Rules for P The The Axiomatic Structure of P Theorems and Derived Rules

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

1.(每题2分,共10分)判断题(若正确,则在题前的括号中打√;否则,打): (a)()若合式公式A是永真式当且仅当合式公式B是永真式,则AB是永真式。 (b)()若合式公式A是可满足的,则~A是不可满足的。 (c)()v((,x)y~(,y)是可满足的 (d)()设P是一个由P系统增加单个合式公式pq作为公理所得到的系统,则P是协调的