Expression 'assets' replaces 'assets and block of assets' in tax provision, altering depreciation classification rules. Substitution in Explanation 3 to section 32(1) replaces the phrase 'the expressions 'assets' and 'block of assets'' with 'the expression 'assets'', narrowing the statutory terminology to a single expressive term and altering the reference to depreciable property and the grouping concept previously denoted as a 'block of assets'.