Bad sequence
= Bad sequence
A bad sequence in a <preorder> is an infinite <sequence> with no indices $i<j$ satisfying $x_i\le x_j$. A <preorder> is a <well-quasi-ordering> precisely when no such sequence exists.
= Bad sequence
A bad sequence in a <preorder> is an infinite <sequence> with no indices $i<j$ satisfying $x_i\le x_j$. A <preorder> is a <well-quasi-ordering> precisely when no such sequence exists.