The appeal relates only to the balance of £130 remaining after subtracting from the £2,016 an amount of £1,886 which the taxpayer expended in the year of income in replacing the cattle destroyed. In making his assessment, the commissioner added the £2,016 to the amount shown in the livestock schedule in the taxpayer's return under sales, and he added the £1,886 to the amount shown under purchases. To describe the £2,016 as proceeds of sale is, of course, inaccurate. In the notice of assessment and the explanatory documents attached to it there was nothing to suggest that the commissioner had relied upon s. 26 (j). For that reason, the Board of Review considered that the commissioner was not entitled to rely upon s. 26 (j) as justifying his action in treating the £2,016 as assessable income; and they referred to certain observations made by Latham C.J. and Starke J. in Danmark Pty. Ltd. v. Federal Commissioner of Taxation [1] . I do not understand those observations to mean more than this, that where there are two provisions of an assessment Act, each giving the commissioner a power to make an assessment, and each creating a liability to tax in the event of the power it confers being exercised, an assessment made in exercise only of the power given by one of those sections cannot be supported as effective under the other. The situation in the present case is quite different. If the £2,016 formed part of the taxpayer's assessable income by reason of s. 26 (j), as I think it did, its inclusion in his assessable income in the course of making the assessment was right, whether or not the commissioner referred to s. 26 (j), and even though he described the amount inaccurately. No conduct on the part of the commissioner could operate as an estoppel against the operation of the Act: cf. Commissioners of Inland Revenue v. Brooks [1] ; Maritime Electric Co., Ltd. v. General Dairies, Ltd. [2] .