When Removal Is Hard

Two-dimensional Mo (二维莫队). Sort as usual, but block both endpoints and order the queries by the resulting pair. Within a block, extend both pointers from a fixed corner and undo the extension after each query.

Rollback Mo (回滚莫队). Sort as usual, but never move a pointer in the direction that would require a removal. Within a block, extend from a fixed left boundary and undo the whole extension after each query.

Mo with modifications (带修莫队). Sort as usual, but add a third pointer over the timeline that walks forward and back. Within a block, roll time to each query's timestamp and undo the whole walk after each query.

Mo on trees (树上莫队). Sort as usual, but move the pointers over an Euler tour so that a subtree becomes contiguous. Within a block, toggle each node on entry and off on exit and undo the whole toggle after each query.