Could someone explain, like just a geometric description, how the space , where is the unit circle in the -plane, is homotopy equivalent to , the one point union of a 2-sphere and a circle. I can't see it.
Could someone explain, like just a geometric description, how the space , where is the unit circle in the -plane, is homotopy equivalent to , the one point union of a 2-sphere and a circle. I can't see it.