Maths WorkshopMaths problems with full solutions
Exercise 568Logic, sets and proofs › RelationsL1Added 3 Nov 2026

Partial orders

#partial order#poset#subsets

Statement

Show that (P(X),⊆)(\mathcal{P}(X),\subseteq) is a partial order.

Hint

Reflexive, antisymmetric, transitive.

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Solution

Reflexive. A⊆AA\subseteq A.

Antisymmetric. A⊆BA\subseteq B and B⊆AB\subseteq A implies A=BA=B.

Transitive. A⊆B⊆C⇒A⊆CA\subseteq B\subseteq C\Rightarrow A\subseteq C.

Not total. For X={1,2}X=\{1,2\}: {1}⊈{2}\{1\}\not\subseteq\{2\} and {2}⊈{1}\{2\}\not\subseteq\{1\}.

Conclusion. (P(X),⊆)(\mathcal{P}(X),\subseteq) is a partial order, not total (for ∣X∣≥2|X|\ge2).