Am a bit confused about the meaning of cardinality. If ## A \subseteq B ##, then is it necessarily the case that ## |A| \leq |B| ##?(adsbygoogle = window.adsbygoogle || []).push({});

I am thinking that since ## A \subseteq B ##, an injection from A to B exists, hence its cardinality cannot be greater than that of B?

But this cannot be correct, since ##\mathbb{Z}## and ##\mathbb{Q}## have the same cardinality?

Where am I wrong?

Thanks!

BiP

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# Cardinality of infinite subset of infinite set

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