Interest on compensation / enhanced compensation

Clause viii to section 56(2) is as follows:

(viii) income by way of interest received on compensation or on enhanced compensation referred to in clause (b) of section 145A;

and clause iv of section 57 (the section providing deduction) is as follows:

(iv) in the case of income of the nature referred to in clause (viii) of sub-section (2) of section 56, a deduction of a sum equal to fifty per cent of such income and no deduction shall be allowed under any other clause of this section.

then how you can say that deduction is only for enhanced compensation??