An exact proof term for the current goal is CD_exp_nat_1 {3} CSNo quaternion_tag_fresh minus_CSNo conj_CSNo add_CSNo mul_CSNo CSNo_0 CSNo_1 minus_CSNo_0 conj_CSNo_0 conj_CSNo_1 add_CSNo_0L add_CSNo_0R mul_CSNo_0L mul_CSNo_1R.