> to denote two completely separate concepts No, same concept ... you're making a mistake that some call "implementation on the brain". That they're the same c

> to denote two completely separate concepts No, same concept ... you're making a mistake that some call "implementation on the brain". That they're the same concept is why you're able to specify a common operation, SelectNotNull. That you had to provide an explicit type constraint that a compiler should be able to infer doesn't change that.