  We investigate the mixing coefficients of interval maps satisfying Rychlik's
conditions. A mixing Lasota-Yorke map is reverse $\phi$-mixing. If its
invariant density is uniformly bounded away from 0, it is $\phi$-mixing iff all
images of all orders are big in which case it is $\psi$-mixing. Among
$\b$-transformations, non-$\phi$-mixing is generic. In this sense, the
asymmetry of $\phi$-mixing is natural.

Dynamical Systems;Probability