IANAL, but you should talk to a lawyer experienced in startups/equity/contracts ASAP. Don't tell your partner that you've talked to a lawyer (mentioning lawyers

IANAL, but you should talk to a lawyer experienced in startups/equity/contracts ASAP. Don't tell your partner that you've talked to a lawyer (mentioning lawyers is a great way to make a conversation go south) - unless your lawyer advises otherwise. You should probably go sort this out and you probably shouldn't apply to YC. I guess you learned a lesson the hard way? (that is, it's really important to have a cofounder you totally trust; I might be totally off here but I would guess you didn't have that close of a relationship with your cofounder).