Prove or disprove either prove or give a counterexample If A

Prove or disprove (either prove or give a counterexample): If A and D are finite sets then |A U B| = |A| + |B|. If f: N rightarrow N is injective then it is bijective. If f: Z rightarrow Z satisfies f o f = f, then f is bijective. If f: Z rightarrow Z satisfies f o f = id, then f is bijective. If A is uncountable and D is countable, there exists a surjective map f:Arightarrow B. If A x D is a denumerable set then either A or D is denumerable. If A is an infinite set then A contains two disjoint denumerable sets. Q (0.1) is denumerable.

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