elim (eq_term_dec U1 U2) [ #H destruct | #HnU12 ]
[ cases HTU1 -HTU1 #HTU1 #_
cases HTU2 -HTU2 #HTU2 #_
/3 width=3 by cprs_div, or_introl/
| @or_intror #H
elim (cpcs_inv_cprs … H) -H #T0 #HT10 #HT20
elim (eq_term_dec U1 U2) [ #H destruct | #HnU12 ]
[ cases HTU1 -HTU1 #HTU1 #_
cases HTU2 -HTU2 #HTU2 #_
/3 width=3 by cprs_div, or_introl/
| @or_intror #H
elim (cpcs_inv_cprs … H) -H #T0 #HT10 #HT20