-theorem height_append (p1) (p2):
- (♯p2+♯p1) = ♯(p1●p2).
-#p1 elim p1 -p1 //
-* [ #n ] #p1 #IH #p2 <list_append_lcons_sn
-[ <height_d_sn <height_d_sn //
-| <height_m_sn <height_m_sn //
-| <height_L_sn <height_L_sn //
-| <height_A_sn <height_A_sn //
-| <height_S_sn <height_S_sn //
+theorem height_append (p) (q):
+ (♯p+♯q) = ♯(p●q).
+#p #q elim q -q //
+* [ #k ] #q #IH <list_append_lcons_sn
+[ <height_d_dx <height_d_dx //
+| <height_m_dx <height_m_dx //
+| <height_L_dx <height_L_dx //
+| <height_A_dx <height_A_dx //
+| <height_S_dx <height_S_dx //