(a)if the cost of the new asset is not less than the ] [net consideration] [Substituted by Act 21 of 1979, Section 8, for certain words (w.e.f. 1.4.1979).][in respect of the original asset, the whole of such capital gain shall not be charged under section 45; [Inserted by Act 29 of 1977, Section 13 (w.e.f. 1.4.1978).]