A new type of bifurcation to chaos is pointed out and discussed. In this bifurcation two unstable fixed points or periodic orbits are created simultaneously with a strange attractor which has a fractal basin boundary. Chaotic transients associated with the coalescence of the unstable-unstable pair are shown to be extraordinarily long-lived.
Grebogi, C., Ott, E., & Yorke, J. A. (1983). Fractal Basin Boundaries, Long-Lived Chaotic Transients, and Unstable-Unstable Pair Bifurcation. Physical Review Letters, 50(13), 935-938. https://doi.org/10.1103/PhysRevLett.50.935