exfalso
case inl.«4»
n : ℕ
h1 : ProblemPredicate n
c : ℕ
h2 : ProblemPredicate' c n
h : (digits 10 c).length = 4
h3 : 4 < 6
⊢ n ≥ 153846
case inl.«4»
n : ℕ
h1 : ProblemPredicate n
c : ℕ
h2 : ProblemPredicate' c n
h : (digits 10 c).length = 4
h3 : 4 < 6
⊢ False