We now show the following improvement on (2).
The basic improvement is the smoothness condition on $G$ given in (6).
The object of this paper is to obtain improvements in two cases, namely for forms of degree 7 and 11.
There has since been a series of improvements, of which we briefly mention the work of Levinson.
The author is grateful to the referee for a number of helpful suggestions for improvement in the article.
The author thanks the referee for recommending various improvements in exposition.
a considerable $\langle$major/marked/radical/remarkable/significant/minor/slight$\rangle$ improvement