From Wikipedia :
In the theory of computational complexity, some algorithms take two-exponential time:
Each Presburger arithmetic decision procedure is provably provable with at least two exponential time
Calculation of the Gröbner basis over the field. In the worst case, the Gröbner basis can have a number of elements that are twice exponential in the number of variables.
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CTL + (, , 2-EXPTIME-complete)
(. ).