比較できないマイケルソンペア

次のMichelsonスクリプトを入力しようとすると、入力エラーが発生します.

 parameter unit;
storage (big_map (pair string address) (list timestamp));
code {CDR; NIL operation; PAIR};
 

 Ill formed type.
At line 2 characters 17 to 37,
comparable type expected.Type pair string address is not comparable.
 

ミシェルソンリファレンスによると、タイプpair ty1 ty2、addressとstringは同等です.私は何かが足りないのですか?この問題を回避する方法はありますか?

When I try to type the following Michelson script, I get a type error.

parameter unit;
storage (big_map (pair string address) (list timestamp));
code {CDR; NIL operation; PAIR};

Ill formed type.
At line 2 characters 17 to 37,
comparable type expected.Type pair string address is not comparable.

According to the Michelson reference, types pair ty1 ty2, address, and string are comparable. Am I missing something? Is there are way to circumvent this issue?