Thank you. Yes, as you say, the "unbounded sum" condition is sufficient, but not necessary. An example that's obvious "by inspection" is just to take an EST f

Thank you. Yes, as you say, the "unbounded sum" condition is sufficient, but not necessary. An example that's obvious "by inspection" is just to take an EST for every value of 2^n ... so take (2^n), (2^n)+1, and (2^n)+2.