Noncommutative Biorthogonal Polynomials

The idea of orthogonal polynomials has been generalized in two ways to achieve new types of polynomials: noncommutative orthogonal polynomials and biorthogonal polynomials. This paper brings these two different generalizations together to present a completely algebraic definition of noncommutative biorthogonal polynomials. It then goes on to obtain recurrence relations for some types of biorthogonal polynomials and concludes with a broad extension of Favard's theorem.