If that’s the license, I couldn’t find it and that would be my mistake. But is a mandatory copyright statement consistent with BSD-3?

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bostr/LICENSE at master · Yonle/bostr

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Yeah that's part of that license. It keeps the author recognized but still allows for any use as long as that statement stays. It adds a third condition just saying you can't use that to promote your project with OG creator.

Yes that is part. Like any BSD OS is carry over from old school.