cross-purchase agreement
buy-sell agreemet
buyout agreement

In what’s called a cross-purchase agreement, the option or obligation belongs to the remaining owners.

The co-founders of the Brooklyn Brewery, also in Williamsburg, relied on their cross-purchase agreement when one of them, Tom Potter, 52, sold 50 percent of the voting stock in 2003 for an undisclosed sum and went to work for a nonprofit.