Arguably a more efficient approach might just be to have a tax that adds on to corporate tax incrementally for every % of market share a company has above say 7-8%. Then dominant companies are incentivised to re-invest in improving their efficiencies rather than just buying/squeezing out competitors. A more evenly spread market would then, as a result, be against regulations that make smaller market participants less competitive, as they'd all be in relatively less table positions.