As it is proven, comparison based sorting has complexity `T(n)=nlogn`. So if we have array of positive integers (not specific one-so that `counting` or `radix` sorts cannot be applied) how to determine appropriate reduction from `Sort` to `SortPositiveNumbers` (for example) in order to prove that there is polynomial and correct transformation and `SortPositiveNumbers` has also lower bound of `nlogn` ? 

Any help would be appreciated.