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CONTINUITY OF DARBOUX FUNCTIONS WITH NICE FINITE ITERATIONS

机译:具有NICE有限项的DARBOUX函数的连续性

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A function that maps intervals into intervals is called a Darboux function. We prove that if g is a continuous function that is non-constant on every non-empty open interval, and f is a Darboux function such that, for every real number x, f~(nx) (x) = g(x) for some positive integer n_x, and the set of all such n_x is bounded, then f is continuous. In the above statement, the hypothesis "the set of all such n_x is bounded" cannot be dropped. We also show that if g is a continuous function that takes a constant value k on some non-empty open interval I and k ∈ I, then there exists a discontinuous Darboux function f : R→R with the property that, for every real number x, f~(nx)(x) = g(x) for some positive integer n_x ≤ 2. In the previous statement, if k is not an element of I, then no conclusion can be drawn about the function f.
机译:将间隔映射为间隔的函数称为Darboux函数。我们证明如果g是在每个非空打开间隔上不恒定的连续函数,并且f是一个Darboux函数,使得对于每个实数x,f〜(nx)(x)= g(x)对于某个正整数n_x,并且所有此类n_x的集合是有界的,则f是连续的。在上面的陈述中,不能删除“所有此类n_x的集合有界”的假设。我们还表明,如果g是在某个非空开放区间I和k∈I上取恒定值k的连续函数,则存在不连续的Darboux函数f:R→R,其性质为,对于每个实数x,对于某个正整数n_x≤2,f〜(nx)(x)= g(x)。在前面的语句中,如果k不是I的元素,则无法得出关于函数f的结论。

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