Escaped assessment notice requirements govern when the Assessing Officer may seek a return before reassessment. Before assessment, reassessment or recomputation under section 147, the Assessing Officer must issue a notice under section 148, subject to section 148A, requiring a return within the prescribed period. The notice can be issued only where the Assessing Officer has information suggesting that income chargeable to tax has escaped assessment, and prior approval is required in cases covered by the notified scheme under section 135A. A return filed beyond the permitted period is not deemed to be a return under section 139.