n:, a, b:. sum(a+bi | i < n)2 = n(a+a+b(n-1)) 

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Definitions	t  T, x:A. B(x), {i..j}, primrec(n;b;c), b, A, Prop, b, , i=j, P  Q, P & Q, P  Q, Unit, , sum(f(x) | x < k), ij, False, AB
Lemmas	ge wf, nat properties, nat wf, eqtt to assert, eqff to assert, iff transitivity, assert of bnot, not functionality wrt iff, assert of eq int, eq int wf, bool wf, bnot wf, not wf, assert wf, primrec wf, int seg wf