 In particular, if formula_7 then formula_8 Give formula_9 and formula_10 their canonical CW-structure, with one 0-cell each, and with one -cell for formula_9 and one -cell for formula_12 Any base-point preserving map formula_13 is then homotopic to a map whose image lies in the -skeleton of formula_14 which consists of the base point only.That is, any such map is nullhomotopic.Let "f"