Ideals are represented as lists of polynomials which generate the ideal.
Like polynomials they
can only be defined or accessed with respect to a basering.
Note: size counts only the non-zero generators of an ideal
whereas ncols counts all generators; see size, ncols.
4.5.1 ideal declarations
4.5.2 ideal expressions
4.5.3 ideal operations
4.5.4 ideal related functions