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A Note on Double Limits

Published online by Cambridge University Press:  20 January 2009

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Let umn, vmn be functions of m and n, vmn being real and positive for all positive values of m and n. Suppose that either vmn increases steadily to infinity with n, or that umn both tend to zero (the latter steadily) as n → ∞, for any fixed value of m. Denote by wmn, and assume that wmn exists for every value of m, being denoted by lm. Then from Stolz' extension of a result proved by Cauchy, and an allied theorem, we have , for all values of m. It follows from Pringsheim's Theorem that if the double limit of exists, being l, then lml as m → ∞.

Type
Research Article
Copyright
Copyright © Edinburgh Mathematical Society 1929

References

1 Or for all values of m and n greater than fixed values, say m 1 and n 1.

2 See Bromwich Infinite Series, pp. 377–378, for both of these.

3 Hereafter when the word “monotonic” is used, the functions concerned are to be regarded as real.