Geodesic
Forcing formulas in Fraïssé structures and classes
Algebra i logika, Tome 57 (2018) no. 5, pp. 567-586
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We come up with a semantic method of forcing formulas by finite structures in an arbitrary fixed Fraïssé class $\mathscr F$. Both known and some new necessary and sufficient conditions are derived under which a given structure $\mathscr M$ will be a forcing structure. A formula $\varphi$ is forced at $\bar a$ in an infinite structure $\mathscr M\Vdash\varphi(\bar a)$ if it is forced in $\mathscr F(\mathscr M)$ by some finite substructure of $\mathscr M$. It is proved that every $\exists\forall\exists$-sentence true in a forcing structure is also true in any existentially closed companion of the structure. The new concept of a forcing type plays an important role in studying forcing models. It is proved that an arbitrary structure will be a forcing structure iff all existential types realized in the structure are forcing types. It turns out that an existentially closed structure which is simple over a tuple realizing a forcing type will itself be a forcing structure. Moreover, every forcing type is realized in an existentially closed structure that is a model of a complete theory of its forcing companion.
Keywords: forcing method, forcing structure, forcing type, existentially closed structure, existentially closed companion.
Mots-clés : Fraïssé class 
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     title = {Forcing formulas in {Fra{\"\i}ss\'e} structures and classes},
     journal = {Algebra i logika},
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     volume = {57},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2018_57_5_a4/}
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A. T. Nurtazin. Forcing formulas in Fraïssé structures and classes. Algebra i logika, Tome 57 (2018) no. 5, pp. 567-586. http://geodesic.mathdoc.fr/item/AL_2018_57_5_a4/

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