Beurling–Lax theorem

In mathematics, the Beurling–Lax theorem is a theorem due to Beurling (1949) and Lax (1959) which characterizes the shift-invariant subspaces of the Hardy space $H^2(\mathbb{D},\mathbb{C})$. It states that each such space is of the form

$\theta H^2(\mathbb{D},\mathbb{C}),$

for some inner function $\theta$.

See also

• H²

References

• Ball, J. A. (2001), "b/b120200", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4
• Beurling, A. (1949), "On two problems concerning linear transformations in Hilbert space", Acta Math. 81: 239–255, doi:10.1007/BF02395019, MR 0027954
• Lax, P.D. (1959), "Translation invariant spaces", Acta Math. 101 (3-4): 163–178, doi:10.1007/BF02559553, MR 0105620
• Jonathan R. Partington, Linear Operators and Linear Systems, An Analytical Approach to Control Theory, (2004) London Mathematical Society Student Texts 60, Cambridge University Press.
• Marvin Rosenblum and James Rovnyak, Hardy Classes and Operator Theory, (1985) Oxford University Press.