elim (sex_sdj_split … ceq_ext … HL 𝐈𝐝 ?) -HL
[ #L0 #HL10 #HL02 |*: /2 width=1 by ext2_refl, sdj_isid_dx/ ] -H1R
lapply (sex_sdj … HL10 f1 ?) /2 width=1 by sdj_isid_sn/ #H
elim (sex_sdj_split … ceq_ext … HL 𝐈𝐝 ?) -HL
[ #L0 #HL10 #HL02 |*: /2 width=1 by ext2_refl, sdj_isid_dx/ ] -H1R
lapply (sex_sdj … HL10 f1 ?) /2 width=1 by sdj_isid_sn/ #H