Hikaku

1. Every cell of an N×N grid takes a number from 1 to N.
2. In every row, every column and every region, each number appears exactly once.
3. Between two neighbouring cells stands a comparison sign. Its point aims at the smaller of the two cells.

A click selects a cell — nothing else. A key sets the number, ⌫ takes it back. The pencil switches to marking mode: the keys then write notes into the selected cell instead of numbers.

The candidates switch fills in every number still possible — once, when you turn it on; after that nothing recalculates. Tidy up removes what no longer fits the numbers you have set and fills the possible candidates in again. Notes of your own that still fit are kept.