Imagine now that the next day Alice regrets selling her half of the company and offers Bob to buy half of his shares from him to get back to the initial situation.
In universe (a) they agree that the company is worth $10mn. Alice pays Bob $5mn and they end both with $5mn in cash and each half of the company is valued at $5mn. Their net wealth is unchanged.
In the nonsensical alternative universe (b) they agree that the company is worth $20mn and Alice pays $10mn to Bob to get back 50% of the company. Alice would be again in the initial situation (no cash and a piece of business worth $10mn) while Bob would have made a large profit ($10mn in cash in addition to half of the company with the same value as before). If all the exchanges between Alice, Bob and the company have been done at fair value how did Bob end in a better situation than Alice? If all the exchanges have been done between Alice, Bob and the company only how can the net profit be explained?
In universe (a) they agree that the company is worth $10mn. Alice pays Bob $5mn and they end both with $5mn in cash and each half of the company is valued at $5mn. Their net wealth is unchanged.
In the nonsensical alternative universe (b) they agree that the company is worth $20mn and Alice pays $10mn to Bob to get back 50% of the company. Alice would be again in the initial situation (no cash and a piece of business worth $10mn) while Bob would have made a large profit ($10mn in cash in addition to half of the company with the same value as before). If all the exchanges between Alice, Bob and the company have been done at fair value how did Bob end in a better situation than Alice? If all the exchanges have been done between Alice, Bob and the company only how can the net profit be explained?