Regression equaltion

I have a two way fixed effect model and I am trying to write a regression equation:
The paper I am referring to has : Bist = αHist + Xistβ + Sstγ + δs + τt + (Error)ist

Other papers I read has "βXist" and more β on the left hand side. I am trying to understand the difference between these two scenarios. How should I know the β is on the right or left side.