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sure; certain; positive; definite
reliable; trustworthy; safe; sound; firm; accurate; correct; exact
If I'm not mistaken; If I remember correctly; If I remember rightly
慥かこの近くに郵便局があったはずです。
I'm sure there was a post office around here.
慥か彼は明日来ると言っていた気がする。
If I'm not mistaken, he said he would come tomorrow.
たしか明日が締め切りだ。
I'm pretty sure the deadline is tomorrow.