-theorem dfr_des_ifr (f) (p) (q) (t1) (t2): t1 ϵ 𝐓 →
- t1 ➡𝐝𝐟[p,q] t2 → ▼[f]t1 ➡𝐢𝐟[⊗p,⊗q] ▼[f]t2.
-#f #p #q #t1 #t2 #H0t1
-* #k * #H1k #Ht1 #Ht2
-@(ex_intro … (↑♭q)) @and3_intro
-[ -H0t1 -Ht1 -Ht2
+theorem dfr_des_ifr (f) (t1) (t2) (r): t1 ϵ 𝐓 →
+ t1 ➡𝐝𝐟[r] t2 → ▼[f]t1 ➡𝐢𝐟[⊗r] ▼[f]t2.
+#f #t1 #t2 #r #H0t1
+* #p #q #k #Hr #H1k #Ht1 #Ht2 destruct
+@(ex4_3_intro … (⊗p) (⊗q) (↑♭q))
+[ -H0t1 -H1k -Ht1 -Ht2 //
+| -H0t1 -Ht1 -Ht2