Well, USPTO is judge and made that determination, just like it does regarding "obviousness"
Anecdote: my technician - a self-professed inventor himself even though I pointed out to him that his "inventions" are unpatentable because they`re just repackaged stuff - thinks that my next-generation inverter invention is obvious, until I remind him that I`ve explained to him its principles at least 5 times yet he still doesn`t quite understand how it works, and nothing that simple exists on the market, and the chance of 100 engineers asked to design an inverter to come up with a similar structure is zero - it`s been like that the last 50-some years.
The Supreme Court is working o the issue of "obviousness". I`d say that if a device or method could be developed "in a clean room environment" that results in a similar or same device/method, then it`s obvious.
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