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Let $k$ be an algebraically closed field and $A, B$ be two finitely generated $k$-algebras. Suppose $B$ is flat over $A$. Let $M$ be a finitely generated $B$-module which is flat over $A$. Is it true that for any $n>0$, the tensor power $M \otimes_B M \otimes_B ... \otimes_B M$ flat over $A$? Note here the tensor product is taken as $B$-modules.

Analogously, is the $n$-th exterior power $M \wedge_B M \wedge_B ... \wedge_B M$ obtained as the quotient of the above tensor power, going to be flat over $A$?

I know that the answer is false when instead of tensor power, I just take tensor product (tensor product over $B$ of two $A$-flat modules flat over $A$?).

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    $\begingroup$ Take $M=E\oplus F$ where $E$, $F$ are $A$-flat but $E\otimes_B F$ isn't. $\endgroup$
    – Laurent Moret-Bailly
    Commented Aug 4, 2016 at 15:54
  • $\begingroup$ Remark: in the case $A=B$, the question about the exterior powers has a positive answer by Lazard's theorem. $\endgroup$
    – js21
    Commented Feb 13, 2017 at 10:27

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