N1Pattern 4
〜や否や／〜や
Formula:
V-る
Examples & key points
その顔を見るや否や、逃げ出しました。
Sono kao o miru ya inaya, nigedashimashita.
The instant he saw that face, he bolted.
や否や is the very instant, with what follows coming immediately
ベルが鳴るや、生徒たちは走り出した。
Beru ga naru ya, seitotachi wa hashiridashita.
The bell rang and the students were off.
Shortened to や it is more archaic still, common in fiction
後ろに自分の意志は置けません。
Ushiro ni jibun no ishi wa okemasen.
Your own deliberate act cannot follow it.
Like たとたん at N2, it reports something sudden