[isabelle] Axclass with multiple type variables?

Dear all,

would there be any way of using multiple type variables in an axclass, e.g. in a cascaded definition like this:

axclass A \<subseteq> type

f :: "'a::A \<Rightarrow> 'b \<Rightarrow> bool"
axclass B \<subseteq> type
f_holds: "f a b"

Here, the error message of course is

*** Multiple type variables in class axiom:
*** f a b
*** At command "axclass".

Is there any solution to establish the above construction in Isabelle?

Thanks in advance,


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