Definition:Tower in Set

From ProofWiki
Jump to navigation Jump to search


Let $X$ be a set.

Let $T$ be any non-empty subset of $X$

Let $c$ be a fixed choice function on the non-empty subsets $T$ of $X$.

Let $\preccurlyeq$ be a well-ordering on $T$.

The well-ordered set $\left({T,\preccurlyeq}\right)$ is a tower in $X$ if and only if, for all $t \in T$:

$t = c \left({X \setminus S_t \left({T}\right)}\right)$

where $S_t \left({T}\right)$ is the initial segment of $T$ determined by $t$.