Horn sentences with (W) and weak Mal'cev conditions

1984 ◽  
Vol 19 (2) ◽  
pp. 217-230 ◽  
Author(s):  
G�bor Cz�dli ◽  
Alan Day
Keyword(s):  
Horn Sentences

scholarly journals Semigroups, Horn sentences and isolic structures

1975 ◽  
Vol 61 (1) ◽  
pp. 87-101
Author(s):  
Erik Ellentuck
Keyword(s):  
Horn Sentences

scholarly journals Horn sentences

1970 ◽  
Vol 1 (4) ◽  
pp. 389-422 ◽  
Author(s):  
Fred Galvin
Keyword(s):  
Horn Sentences

Horn sentences excluding a prime

1986 ◽  
Vol 22 (1) ◽  
pp. 94-96 ◽  
Author(s):  
S. Tulipani
Keyword(s):  
Horn Sentences

Sheaves and normal submodels

1977 ◽  
Vol 42 (2) ◽  
pp. 241-250 ◽  
Author(s):  
Richard Mansfield
Keyword(s):  
Model Theory ◽  
Heyting Algebra ◽  
Global Section ◽  
Principal Result ◽  
Traditional Model ◽  
Boolean Valued Model ◽  
Definition Of ◽  
Interesting Generalization ◽  
Horn Sentences

Ellerman, Comer, and Macintyre have all observed that sheaves are an interesting generalization of models and are deserving of model theoretic attention. Scott has pointed out that sheaves are Heyting algebra valued models. The reverse does not hold however since almost no genuine Boolean valued model is a sheaf.In §1 we shall review the definition of a sheaf and prove a theorem about Boolean valued models using the sheaf construction. In §2 we shall be concerned with the set of sentences preserved by global sections. Our principal result is that global section sentences are also normal submodel sentences. (We define as a normal submodel of if is a submodel of and every point of B − A can be moved by an automorphism of which fixes each point of A.) In §3 we prove that every normal submodel sentence is the negation of a disjunction of Horn sentences and that the set of normal submodel sentences is r.e. but not recursive. §3 involves only traditional model theory and can be read independently of the first two sections.

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