に違いない
Usage
(V/いA/なA~~-だ~~/N~~-だ~~) + に違いない Used to express the speaker's strong conviction based on some solid foundation
Examples
私の傘がない。誰かが持って行ったに違いない
My umbrella is not here. Someone must have taken it
あの店はいつも混んでいるから、安いに違いない
That restaurant is always packed - it must be cheap