Foucault and what he read by the Frankfurt School

In a number of places Foucault mentions his debt to the Frankfurt
School. And I am wondering what this debt really consists in. Does anyone
here have any information on what it is Foucault read by the FS? On a
similar point, Foucault says he was deeply influenced by Heidegger,
but that he never read _Being and Time_. Does anyone have any ideas what
else it is Foucault might have been looking at? Perhaps Heidegger's
_Nietzsche_? He does say that it was Heidegger and Nietzsche *together*
that provided him with a big shock.

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