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In mathematics, a devil's staircase is any function f(x) defined on the interval [a,b] that has the following properties:
- f(x) is continuous on [a,b].
- there exists a set N of measure 0 such
that for all x outside of N the derivative f
′(x) exists and is zero.
- f(x) is nondecreasing on [a,b].
- f(a) < f(b).
A standard example of a devil's staircase is the Cantor function,
which is sometimes called "the" devil's staircase. There are, however, other functions that have been given that name. One is
defined in terms of the circle
map.
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