I want to know the answer to the following question:
What can imperfective verb undergo to make other imperfective verbs?
All the background I'm provided with is that "In suffix pairs, a different infinitive ending is added to the perfective stem; for example, the perfective verbs koupit (to buy) and prodat (to sell) have the imperfective forms kupovat and prodávat.". Is that enough to answer the question?
Answer: no