changeset 66490 | cc66ab2373ce |
parent 65578 | e4997c181cce |
child 66836 | 4eb431c3f974 |
--- a/src/HOL/Set_Interval.thy Wed Aug 23 14:37:22 2017 +0200 +++ b/src/HOL/Set_Interval.thy Wed Aug 23 18:28:56 2017 +0200 @@ -1894,6 +1894,9 @@ subsection \<open>The formula for geometric sums\<close> +lemma sum_power2: "(\<Sum>i=0..<k. (2::nat)^i) = 2^k-1" +by (induction k) (auto simp: mult_2) + lemma geometric_sum: assumes "x \<noteq> 1" shows "(\<Sum>i<n. x ^ i) = (x ^ n - 1) / (x - 1::'a::field)"