86. (1) Where, at the time of assessment of a firm, it is found that a charge has occurred in the constitution of the firm, the assessment shall be made on the firm as constituted at the time of making the assessment : Provided that- (a) the income of the years shall, for the purpose of inclusion in the total income of the partners, be apportioned between the partners who, in such income year, were entitled to receive the same; and (b) when the tax assessed upon a partner cannot be recovered from him, it shall be recovered from the firm as constituted at the time of making the assessment. (2) For the purpose of this section, there is a change in the constitution of a firm- (a) where all the partners continue with a change in their respective shares or in the shares of some of them, or (b) where one or more persons who were partners continue to be so with a change by cessation of one or more partners or addition of one or more new partners.