Finding inclusion-maximal components from the complete subset table

On this page
  1. Goal and scope
  2. Givens and symbols
  3. Rules and sources
  4. Main derivation
  5. Substeps and lemmas
  6. Reverse audits
  7. Error controls and negative controls
  8. Result and limitations
  9. Verification and source binding

← Guide index · Original MKO

derivation-mko-topological-connected-component-01 · ocme-new142-reader-adoption-20261021

Goal and scope

Find every component of X={a,b,c}, tau={empty,{a},{b,c},X}.

Use each induced topology, not a graph; do not extrapolate finite clopen components.

Givens and symbols

  • sets
  • topology
  • definition_here
  • G1 — X={a,b,c}, tau={empty,{a},{b,c},X}; the empty space is connected by convention.
  • C_x — component containing x
  • \mathcal C — all connected subsets

Rules and sources

  • mko_definition · cited — Finite families enumerate every induced subspace and connected subset. The union of all connected subsets containing x is its unique inclusion-maximal component. Then check that the components are pairwise equal or disjoint, cover X and are closed in the stated finite model. Finitely many closed components also make each component open, a finite-specific conclusion. In a general space components need not be open: in the rational subspace of the real line they are singletons and are not open. Do not substitute globally largest cardinality, graph components or a different structure on the same carrier. · mko-topological-connected-component
  • sets · prerequisite — Compute unions, intersections, complements, inclusion and preimages element by element.
  • topology · prerequisite — A topology contains empty and whole sets and is closed under arbitrary unions and finite intersections; a finite family admits exhaustive checks.
  • definition_here · prerequisite — Subspace opens are ambient-open intersections; a connected subset has no nontrivial relative-open separation; the component of x is the union of all connected subsets containing x, equivalently the inclusion-maximal connected subset.

Main derivation

S01 · implies

Before

\{a\}\cap\{b,c\}=\varnothing,\quad\{a\}\cup\{b,c\}=X

After

\tau\text{ is a topology}

Conditions: none

Rule: topology · Uses: G1

Leaf basis: topology

Apart from the complementary pair, operations with empty and whole stay in the family; every union/intersection axiom follows.

S02 · definition

Before

\mathcal P(X)

After

\varnothing,\{a\},\{b\},\{c\},\{a,b\},\{a,c\},\{b,c\},X

Conditions: none

Rule: definition_here · Uses: G1

Leaf basis: definition_here

List all eight subsets before computing their induced topologies.

S03 · implies

Before

Y=\varnothing,\{a\},\{b\},\{c\}

After

\tau_\varnothing=\{\varnothing\},\quad\tau_{\{p\}}=\{\varnothing,\{p\}\}

Conditions: none

Rule: sets · Uses: S01, S02

Leaf basis: sets

The four small subsets have the listed induced topologies and no nontrivial separation.

S04 · implies

Before

Y=\{a,b\},\{a,c\}

After

\tau_{\{a,b\}}=\mathcal P(\{a,b\}),\quad\tau_{\{a,c\}}=\mathcal P(\{a,c\})

Conditions: none

Rule: sets · Uses: S01, S02

Leaf basis: sets

Ambient intersections give two-point discrete topologies, each separated by its two singletons and therefore disconnected.

S05 · implies

Before

Y=\{b,c\},\ X

After

\tau_{\{b,c\}}=\{\varnothing,\{b,c\}\};\quad X=\{a\}\sqcup\{b,c\}

Conditions: none

Rule: sets · Uses: S01, S02

Leaf basis: sets

The induced topology on {b,c} is indiscrete and connected; the two complementary nonempty opens explicitly separate X.

S06 · definition

Before

\mathcal C=\{\varnothing,\{a\},\{b\},\{c\},\{b,c\}\}

After

C_a=\bigcup\{A\in\mathcal C:a\in A\}=\{a\};\quad C_b=C_c=\{b,c\}

Conditions: none

Rule: definition_here · Uses: S03, S04, S05

Leaf basis: definition_here

Unite all connected subsets containing the given point, obtaining the unique inclusion-maximal candidates.

S07 · implies

Before

\{C_a,C_b\}=\{\{a\},\{b,c\}\}

After

C_a\cap C_b=\varnothing,\quad C_a\cup C_b=X

Conditions: none

Rule: sets · Uses: S06

Leaf basis: sets

The distinct components are disjoint and cover the entire carrier.

S08 · implies

Before

X\setminus C_a=C_b\in\tau,\quad X\setminus C_b=C_a\in\tau

After

C_a,C_b\text{ both closed and open}

Conditions: none

Rule: sets · Uses: G1, S07

Leaf basis: sets

Both components are closed and open in this finite model; this does not assert general components are open.

Substeps and lemmas

No substeps in this guide.

Reverse audits

  • S08 · premise_audit · G1, S07 — In Q components are singletons but not open: an intermediate irrational separates any two rationals, while every rational neighborhood contains other rationals.
  • S07 · premise_audit · S06 — The duplicate C_c=C_b is normalized, not counted as a third component.
  • S06 · premise_audit · S03, S04, S05 — The smaller {a} is maximal: the larger {b,c} does not contain it.
  • S05 · premise_audit · S01, S02 — Connectedness has now been decided for all eight subsets.
  • S04 · premise_audit · S01, S02 — The complete four-set power sets are specified, rather than inferred from cardinality.
  • S03 · premise_audit · S01, S02 — The declared convention handles empty, and a singleton has only one nonempty set.
  • S02 · premise_audit · G1 — Maximality must use all candidates, not just large-looking sets.
  • S01 · premise_audit · G1 — The four-member list is complete.

Error controls and negative controls

Complete subset table

Check all eight induced subspaces before inclusion-maximality.

Maximal is not largest

Maximal means no proper connected superset, not largest cardinality.

  • Only a largest-cardinality connected set is a component. → reject — {a} is smaller but remains inclusion-maximal.
  • {a,b} is connected. → reject — Its induced two-point discrete topology has a separation.
  • Components are open in every space. → reject — The singleton components of Q are not open, as justified at S08.

Result and limitations

The components {a} and {b,c} partition X and are clopen in this finite space.

    Verification and source binding

    0 declared checks for this guide; only the listed expressions are covered.

    • source commit: b1b2f1dcf8c50d67a93fe52d95f8eef7b3abba9f
    • adopted source SHA-256: 6e7ae0b999704533941449659c621f44afd0b89cb6a393c46fd149e31af15455
    • original source SHA-256: f483b0fb384b4a7aa4bbe6cef26217d76cd52ab525b06d887513dadcd82709d5
    • Lean: NOT_RUN · independent AI: SCOPED_LEAD_AND_BILINGUAL_CONTEXT_REVIEW

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