I've co-authored a HOPL IV paper and given lots of talks, do some searches and you will find them (https://dl.acm.org/doi/pdf/10.1145/3386327). There's no doubt about this. I knew of Self and liked it but did not have time for multiple parent* slots. I didn't even have time to expose the unstratified (meta- in base-level) __proto__ property until 1997 in SpiderMonkey. I was aiming at Self + Scheme-ish (definitely "ish") first class functions because I had to interop with Java.