@Article{Seidel90a,
    author = {E. Seidel and S. Iyer},
    title = {Black Hole Normal Modes: A WKB Approach. IV. Kerr Black Holes},
    journal = {Phys. Rev. D},
    year = {1990},
    key = {Seidel90a},
    volume = {41},
    pages = {374}
}