I'd like to use a comparator to act when e.g. a
testforblock command block attached to a button triggers. But the comparator changes its state only when the button is pressed after the test result changes, while I'd like to have a short pulse if nothing changed, i.e.
previous command block state | new command block state | desired output on | off | off off | on | on on | on | briefly off, then on off | off | briefly on, then off
How can this be achieved?