Almost disjointness number
= Almost disjointness number
{title2=$\mathfrak a$}
The least size of an infinite <maximal almost disjoint family on omega>. <Zorn lemma> extends an infinite disjoint family to a maximal one; thus $\mathfrak a\le2^{\aleph_0}$. The <bounding-to-almost-disjointness inequality> supplies $\mathfrak b\le\mathfrak a$.