The call type(expr, algnumext) checks to see if expr is an algebraic number extension.

An algebraic number extension is a root of a univariate polynomial with algebraic number coefficients, specified by a RootOf.

For example, the algebraic number  could be specified as RootOf(z^2-2, z).

The expression type(expr, algnumext) is equivalent to the expression:  type(expr, RootOf) and type(expr, algnum) .