Theoria. Revista de Teoría, Historia y Fundamentos de la Ciencia

Volume 15, Issue 3, Septiembre 2000

A Preservation Theorem for Equality-Free Horn Sentences

We prove the following preservation theorem for the Horn fragment of Equality-free Logic: Theorem 0.1. For any sentence σ ϵ L, the following are equivalent: i ) σ is preserved under Hs , Hs -1 and PR . i i ) σ is logically equivalent to an equality-free Horn sentence.