have h4 : 6 * 10 ^ 4 + c = 4 * (10 * c + 6) := by rw [h3, h2.right, h2.left]
c n : ℕ
h1 : (digits 10 c).length = 4
h2 : ProblemPredicate' c n
h3 : 6 * 10 ^ 4 + c = 6 * 10 ^ (digits 10 c).length + c
⊢ False
c n : ℕ
h1 : (digits 10 c).length = 4
h2 : ProblemPredicate' c n
h3 : 6 * 10 ^ 4 + c = 6 * 10 ^ (digits 10 c).length + c
h4 : 6 * 10 ^ 4 + c = 4 * (10 * c + 6)
⊢ False