Quasi-component
= Quasi-component
{title2=$Q(x)=\bigcap\{U:x\in U,\ U\text{ clopen}\}$}
The <quasi-component> of a point is the <intersection> of its <clopen> neighborhoods. Its <connected component> is always contained in it: a <connected set> meeting a <clopen> set cannot also meet its complement. Equality need not hold in noncompact <Hausdorff> spaces. The <Šura-Bura lemma> proves equality in <compact Hausdorff spaces>.