Induced and non-induced poset saturation problems

A subfamily $\mathcal{G}\subseteq \mathcal{F}\subseteq 2^{[n]}$ of sets is a non-induced (weak) copy of a poset $P$ in $\mathcal{F}$ if there exists a bijection $i:P\to \mathcal{G}$ such that $p{\le }_{P}q$ implies $i(p)\subseteq i(q)$. In the case where in addition $p{\le }_{P}q$ holds if and only if $i(p)\subseteq i(q)$, then $\mathcal{G}$ is an induced (strong) copy of $P$ in $\mathcal{F}$. We consider the minimum number $sat(n,P)$ [resp.
$sa{t}^{\ast }(n,P)$] of sets that a family $\mathcal{F}\subseteq 2^{[n]}$ can have without containing a non-induced [induced] copy of $P$ and being maximal with respect to this property, i.e., the addition of any $G\in 2^{[n]}\setminus $\mathcal{F}$$createsanon-induced[induced]copyof$P$. We prove for any finite poset $P$ that $sat(n,P)\le 2^{\mathrm{\mid }P\mathrm{\mid }-2}$, a bound independent of the size $n$ of the ground set. For induced copies of $P$, there is a dichotomy: for any poset $P$ either $sa{t}^{\ast }(n,P)\le K_P$ for some constant depending only on $P$ or $sa{t}^{\ast }(n,P)\ge {\log }_{2}n$. We classify several posets according to this dichotomy, and also show better upper and lower bounds on $sat(n,P)$ and $sa{t}^{\ast }(n,P)$ for specific classes of posets. Our main new tool is a special ordering of the sets based on the colexicographic order. It turns out that if $P$ is given, processing the sets in this order and adding the sets greedily into our family whenever this does not ruin non-induced [induced] $P$-freeness, we tend to get a small size non-induced [induced] $P$-saturating family.