A Remark on the Existence of a Denumerable Base for a Family of Functions
Fritz Rothberger · Canadian Journal of Mathematics · 1952
A family F of functions is said to have a denumerable base if there exists a sequence of functions {fn(x)} (not necessarily ∈ F) such that any function f ∈ F is the limit of a subsequence of {fn (x)}. The domain X of a function f(x) is the set of x´s for which f(x) is defined ; we say f(x) is a function on X. A dyadic function is a function taking only the values 0 and 1.