rcases j with ⟨j,hj'⟩
case mk
m n : Nat
j : Fin m
hj : ↑j < n
i : Nat
hi' : i < m
hi : ↑{ val := i, isLt := hi' } < n
h : restrict { val := i, isLt := hi' } hi = restrict j hj
⊢ { val := i, isLt := hi' } = j
case mk.mk
m n i : Nat
hi' : i < m
hi : ↑{ val := i, isLt := hi' } < n
j : Nat
hj' : j < m
hj : ↑{ val := j, isLt := hj' } < n
h : restrict { val := i, isLt := hi' } hi = restrict { val := j, isLt := hj' } hj
⊢ { val := i, isLt := hi' } = { val := j, isLt := hj' }