[brudgers]

My personal opinion is that if you are negotiating with a cofounder then the relationship may already be off on the wrong foot.

Cofounders should be figuring out what the other person wants and needs, not what they can get. Treating the startup as a finite pie just doesn't make sense.

If it must be addressed for the sake of fairness, any sort of previous IP should be handled as a loan from the new company with terms highly favorable to the new company's growth, e.g. a note payable in four years with a low interest rate because if the idea has significant value the payoff from the new company's value will be significantly greater than the loan amount, and if it has little value, then the company will probably be defunct when the note comes due.

With two of you, it should be 50-50 with a vesting schedule or walk away.