Introduction and main results Conventions and notation Semisimple Hopf algebras The Nichols-Richmond theorem Quotient coalgebras Braided Hopf algebras Cocycle deformations of some Hopf algebras Dimension $24$ Dimension $30$ Dimension $36$ Dimension $40$ Dimension $42$ Dimension $48$ Dimension $54$ Dimension $56$ Appendix A. Drinfeld double of $H_8$ Appendix. Bibliography.