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A New Metatheorem and Subdirect Product Theorem for L-Subgroups
Published in Fuzzy Information and Engineering, 2018
Naseem Ajmal, Iffat Jahan
Let be two expressions in where H and K are subsets of G and the operation is the natural extension of the binary operation given by . In view of Lemma 3.6 and by the isomorphism chi from to , we have
Thus As L is a complete dense chain, the natural extension is commutative. So the metatheorem applies and this equality holds for corresponding L-class also. That is
Therefore .
Axiomatic and dual systems for constructive necessity, a formally verified equivalence
Published in Journal of Applied Non-Classical Logics, 2019
Lourdes del Carmen González-Huesca, Favio E. Miranda-Perea, P. Selene Linares-Arévalo
This problem has been discussed since long time ago. To ensure the validity of the deduction theorem, one usually needs to restrict the definition of derivation or to generalise the statement of this important metatheorem. See for example the works of Zeman (1973, chapter 12) and Perzanowski (1973) (see also the survey Porte, 1982 and Fitting, 2007 for semantical deduction theorems). In this work, we prefer to follow the more recent Hakli and Negri (2012): to validate the deduction theorem we only need to give a precise definition of derivability from assumptions in an axiomatic framework.