Let n be given.
Assume Hn IH.
Apply IH to the current goal.
rewrite the current goal using
add_nat_SR m n Hn (from left to right).
rewrite the current goal using
tuple_2_0_eq (from left to right).
rewrite the current goal using
tuple_2_1_eq (from left to right).
Apply andI to the current goal.
∎