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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. LOMI, 1974 Volume 40, Pages 30–37 (Mi znsl2679)

What does the law of the exeluted middle follow from?

V. Ya. Kreinovich


Abstract: Theories considered contain Heyting arithmetic and the axiom of existence of functions 1.4. Elementary theory of real numbers is constructed along the usual lines (e.g.[4]). It is proved that the law of excluded middle (as a scheme for arithmetic formulae) follows from the statements: the equality of real numbers is decidable; every non-decreasing bounded sequence converges; every partial function can be extended to a total one. The following three theorems are equivalent modulo Markov principles a) decidability of equality, b) the above-mentioned theorem about non-decreasing sequences, c) Bolzano–Weierstrass theorem that every bounded sequence has a convergent subsequence. Lebesgue's theorem that every denumerable open covering of [0,1] contains a finite subcovering follows from each one of a)–c) and is weaker than any of them.

UDC: 51.01



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