@article {IOPORT.50230801,
    author       = {Guibas, Leonidas J. and Sharir, Micha and Sifrony, Shmuel},
    title        = {On the general motion-planning problem with two degrees of freedom},
    year         = {1989},
    journal      = {Discrete & Computational Geometry},
    volume       = {4},
    pages        = {491-521},
    doi          = {10.1007/BF02187744},
    identifier   = {50230801},
}