User:IssaRice/Computability and logic/Semantic completeness

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Semantic completeness is sometimes written as: if Σ⊨ϕ, then Σ⊢ϕ.

Semantic completeness differs from negation completeness.

Definition

I want to make sure all these definitions are saying the same thing, so let me list some from several textbooks so I can explicitly compare.

Smith's definition: a logic is semantically complete iff for any set of wffs Σ and any sentence ϕ, if Σ⊨ϕ then Σ⊢ϕ.[1]

Leary/Kristiansen's definition: A deductive system consisting of logical axioms Λ and a collection of rules of inference is said to be complete iff for every set of nonlogical axioms Σ and every L-formula ϕ, if Σ⊨ϕ, then Σ⊢ϕ.[2]

References

  1. ↑ Peter Smith. An Introduction to Godel's Theorems. p. 33.
  2. ↑ Leary; Kristiansen. A Friendly Introduction to Mathematical Logic. p. 74.