The Supreme Court's Constitution Bench in Dilip Kumar (2018) held that ambiguity in a tax exemption notification is construed in favour of the Revenue, overruling Sun Export Corporation.
U.P. promised new sugar units a three-year sales-tax exemption; Motilal Padampat raised loans and built a plant, then the State resiled. The 1979 ruling on promissory estoppel against the Government.