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an exercise in convergencePublished online by Cambridge University Press: 01 August 2016
For positive x, define the sequence of functions {hn(x)} thus:

So, for example,
x appearing 3 times,
and
x appearing 5 times.
The hyperexponential function is then defined as

for those values of x for which this limit exists. Since an infinite number of operations are involved, we clearly need to study carefully the question of convergence.