Notice of demand requires payment of specified tax; special timing rules apply for start up equity transfers. Section 156 requires the Assessing Officer to serve a notice of demand in the prescribed form specifying any tax, interest, penalty, fine or other sum payable; certain statutory intimations are deemed to be notices of demand. A special rule makes tax or interest on income from specified securities or sweat equity shares allotted by an eligible start up payable by the assessee within a limited period linked to the earliest of a post assessment expiry, the sale of the share, or cessation of employment with the allotting employer.