How to find an uncountable subset of $P(\mathbb{N})$ such that every two elements of it can be compared. In fact, give an uncountable subset of $P(\mathbb{N})$ such that has totality property. We mean by $P(\mathbb{N})$, the powerset of natural numbers set $\mathbb{N}$.
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See also: http://math.stackexchange.com/questions/253192/chain-of-length-2-aleph-0in-p-mathbbn-subseteq – Martin Sleziak Jun 02 '15 at 09:51
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As mentioned in Uncountable chains (in the question itself), one can do this as follows:
Pick a bijection between $\mathbb{N}$ and $\mathbb{Q}$ so it suffices to find such a chain in the powerset of $\mathbb{Q}$. But $\mathbb{Q}\subseteq\mathbb{R}$ so for any real number $r$ we can define the subset $\Gamma_r = \{x\in\mathbb{Q}\mid x < r\}$. This then defines an injective order-preserving map from $\mathbb{R}$ to $\mathcal{P}(\mathbb{Q})$ (given by $r\mapsto \Gamma_r$), which gives us the uncountable chain.

Tobias Kildetoft
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