| #f1 #I1 #L1 #V1 #Hf1 #IH #I2 #L2 #V2 *
[ -IH #HL12 lapply (drops_fwd_isid … HL12 ?) -HL12 //
#H destruct #g1 #Hgf1 >(injective_next … Hgf1) -g1
- /2 width=3 by sle_refl, ex2_intro/
+ /3 width=3 by sle_refl, ex2_intro/
| -Hf1 #n #HL12 lapply (drops_inv_drop1 … HL12) -HL12
#HL12 #g1 <tls_xn <tl_next_rew #Hgf1 elim (IH … HL12 … Hgf1) -IH -HL12 -Hgf1
/2 width=3 by ex2_intro/