When does a continuous map have chaotic dynamics in a set Q? More specifica
lly, when does it factor over a shift on M symbols? This paper is an attemp
t to clarify some of the issues when there is no hyperbolicity assumed. We
find that the key is to define a "crossing number" for that set Q. If that
number is M and M > 1, then Q contains a compact invariant set which factor
s over a shift on M symbols.