have m1_n'_runs : m1.val n' = some x := m1.property n x h2 n' h
case some
α β : Type
m1 : Computation α
m2 : α → Computation β
n : Nat
v : β
n' : Nat
x : α
h1 : Subtype.val (m2 x) n = some v
h : n' ≥ n
h2 : Subtype.val m1 n = some x
⊢ (match Subtype.val m1 n' with
    | none => none
    | some a => Subtype.val (m2 a) n') =
    some v
case some
α β : Type
m1 : Computation α
m2 : α → Computation β
n : Nat
v : β
n' : Nat
x : α
h1 : Subtype.val (m2 x) n = some v
h : n' ≥ n
h2 : Subtype.val m1 n = some x
m1_n'_runs : Subtype.val m1 n' = some x
⊢ (match Subtype.val m1 n' with
    | none => none
    | some a => Subtype.val (m2 a) n') =
    some v