Advanced competition between aspects
See why an imperfective past can report a factually completed event.
Кто открывал окно? can ask whether the activity/fact occurred, while Кто открыл окно? targets one specific resultant opening. An imperfective can also appear when a result was later reversed.
- Fact-of-action questions can favour imperfective.
- Specific result questions can favour perfective.
- An annulled result is a discourse use, not an inherent imperfective meaning.
Mini-check
Which question most directly targets the agent of one resultant opening?
Annulled result
Я открывал окно, но потом закрыл reports that opening occurred while making the later reversal relevant.