An introduction to basic arithmetic

We study Basic Arithmetic BA, which is the basic logic BQC equivalent of Heyting Arithmetic HA over intuitionistic logic IQC, and of Peano Arithmetic PA over classical logic CQC. It turns out that The Friedman translation is applicable to BA. Using this translation, we prove that BA is closed under a restricted form of the Markov rule. Moreover, it is proved that all nodes of a finite Kripke model of BA are classical models of I there exists(+)(1), a fragment of PA with Induction restricted to the formulas made up of there exists, boolean AND and/or boolean OR. We also study an interesting extension of BQC, called EBQC, which is the extension by the axiom schema inverted perpendicular -> perpendicular to double right arrow perpendicular to. We show that this extension behaves very like to IQC, and the corresponding arithmetic, EBA shows similarities to HA.