## When flatness of $B$ over $A$ implies flatness of $B$ over $C$, where $A \subseteq C \subseteq B$ December 1

Assume $A \subseteq C \subseteq B$ are integral domains, with $B$ flat over $A$.Generally, $B$ is not necessarily flat over $C$.For example, see van den Essen's book "Polynomial Automorphisms and the Jacobian Conjecture", page 294, Exercise 4: $