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two days before yesterday; three days back (ago)
一昨昨日に届いた荷物を受け取った。
I received the package that arrived three days ago.
一昨昨日からずっと雨が降っている。
It has been raining since three days ago.
一昨昨日に起きた出来事をようやく思い出した。
I remembered what happened three days ago.