Abstract
Let f be a real-valued function on R. For any interval I, the quantity
is called the oscillation of f on I. For any fixed x, the function ω((x − δ, x + δ)) decreases with δ and approaches a limit
called the oscillation of f at x. ω(x) is an extended real-valued function on R. Evidently, ω(x0) = 0 if and only if f is continuous at x0. When it is not zero, ω(x0) is a measure of the size of the discontinuity of f at x0.
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© 1971 Springer-Verlag New York
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Oxtoby, J.C. (1971). Functions of First Class. In: Measure and Category. Graduate Texts in Mathematics, vol 2. Springer, New York, NY. https://doi.org/10.1007/978-1-4615-9964-7_7
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DOI: https://doi.org/10.1007/978-1-4615-9964-7_7
Publisher Name: Springer, New York, NY
Print ISBN: 978-0-387-05349-3
Online ISBN: 978-1-4615-9964-7
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