(*** at_mono *)
theorem fr2_nat_mono (f) (l):
- â\88\80l1. @â\9d¨l, fâ\9d© â\89\98 l1 â\86\92 â\88\80l2. @❨l, f❩ ≘ l2 → l1 = l2.
+ â\88\80l1. @â\86\91â\9d¨l, fâ\9d© â\89\98 l1 â\86\92 â\88\80l2. @â\86\91❨l, f❩ ≘ l2 → l1 = l2.
#f #l #l1 #H elim H -f -l -l1
[ #l #x #H <(fr2_nat_inv_empty … H) -x //
| #f #d #h #l #l1 #Hld #_ #IH #x #H