An internal characterisation of radiality

In this paper, we will investigate how radiality occurs in topological spaces by considering neighbourhood bases generated by nests. We will define a new subclass of radial spaces, called the independently-based spaces, that contains LOTS, GO-spaces and spaces with well-ordered neighbourhood bases. We show that first-countable spaces are precisely the independently-based, strongly Fr'echet spaces and we give an example of a Fr'echet-Urysohn space that is neither independently-based nor strongly Fr'echet.