X, Y, Z are siblings who inherited a IO-storey building from their parents. They agreed in writing to maintain it as a co-owned property for leasing out and to divide the net profits among themselves equally for a period of 20 years. On the 8th year, X wanted to get out of the co-ownership so he could get his 1/3 share in the property. Y and Z refused, saying X is bound by their agreement to keep the co-ownership for 20 years. Are Y and Z correct? Explain.