# Fixed variable in Groth16

In the paper On the Size of Pairing-based Non-interactive Arguments by Jens Groth, it is always referred in the equations to satisfy that $$a_0 = 1$$ and the others $$a_1, ..., a_m \in \mathbb{F}$$.

I am not sure I understand this specification, as we can always set $$a_0$$ later to 1 if needed. I first thought it was to introduce the constant 1 for the arithmetic circuit basic operation but I am wondering now if this specific value has another use.