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Since the last two proofs are evident, I will focus on the first.
The foundational principle for the proof is that "multiplicity follows upon composition." As an example, if we ask what distinguishes Socrates from other men. Surely, it is not his humanity. For, all men have humanity. Rather, it must be something added upon and beyond his humanity. Yet, if we were to imagine that Socrates' Socratesness was identical to Socrates' humanity, we would have to admit that there was only one man. For, if there was another man, then he would be Socrates, which would be absurd. For, he would not be other. In a similar way, since God IS His Divinity, there can be no other God.