PrefixSums P3
Revert "PrefixSums P3"

This reverts commit 22c2c5b8c51ba47df5952d52f797ea0fecbcd42e.
Revert "Revert "PrefixSums P3""

This reverts commit 43af926d7a7bdf44c9c2bbf12c5adf8d7b3dc226.