Subalgebras of the univariate polynomial algebra
In previous work we have shown that any subalgebra A⊆K[x] of finite codimension n can be described by a finite set Sp(A), called the subalgebra spectrum of A, together with n defining conditions. In this paper we show that a similar result applies to subalgebras of infinite codimension. We also develop new tools for the case of finite codimension. One of them is to introduce an ideal I(A) in A of
