Let's say the code for Lx can call into Ly code if x > y, so in your example L3 code calls L1.
I don't follow. Are you saying Kraken and River are L3s? I'm mostly confused because you objected to calling WBTC L2 but seem to be making an exception for a different custodial system (mints, and now maybe CEXes as well?)
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As I have written in the reply to niftynei, "In my mind what makes a layer is the number of participating entities". So yes, if Kraken, River and some other exchanges allow users to pay each other via LN, then I'd say they form an L3.
I object to calling WBTC L2 because there's only one BitGo, but if there would be 100 different custodians I'd say they form an L2.
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Ok. I don't consider the number of trusted third parties involved to be what distinguishes between what is and isn't a distinct "layer" on bitcoin but to each their own!
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