On the relation between classical and construetive analysis
M. G. Gelfond
Abstract:
The relation of the classical and constructive variants of development of differential and integral calculus is investigated in this paper. A formal language
$\Omega$ for this calculus and a class
$K$ of
$Q$-sentences are described such that the provability of a formula
$F$ from
$K$ in certain classical calculus
$A$ implies the constructive validity of a natural constructive interpretation of
$F$. The language
$\Omega$ contains in particular the variables for real numbers and real functions which under constructive interpretation became variables for recursive real numbers and uniformly continuous recursive real functions.
The well-known examples show that
$K$ cannot include all normal (that is
$\exists,V$-free) sentences of
$\Omega$. Main restrictions are of the type: if
$F\in K$, then for every negative occurence of a formula
$\forall x B(x)(x\operatorname{real})$ in
$F$ the statement
$\ll$ the set
$\{x:B(x)\}$ is closed
$\gg$ is provable in the calculus
$A$.
The class
$K$ proved to be rasher broad; it contains a considerable number of theorems (for example differential and integral inequalitiesi uniqueness theorems and so on) whose conventional classical proofs are essentially non-constructive.