How$$ does an$$ oligopoly structure affect$$ consumer$$ welfare and$$ market efficiency in$$ the long$$ term,$$ particularly$$ in$$ terms$$ of$$ pricing,$$ product$$ variety,$$ and$$ innovation?$$ What regulatory$$ measures could$$ be introduced to prevent collusion and promote competition, while$$ ensuring$$ that$$ firms in$$ the oligopoly$$ remain incentivized to$$ invest in quality$$ and innovation?