Disk algebra
（重定向自Disc algebra）
In functional and complex analysis, the disk algebra A(D) (also spelled disc algebra) is the set of holomorphic functions
where D is the open unit disk in the complex plane C, f extends to a continuous function on the closure of D. That is,
where 
denotes the Banach space of bounded analytic functions on the unit disc D (i.e. a Hardy space).
When endowed with the pointwise addition,
(f+g)(z)=f(z)+g(z),
and pointwise multiplication,