fn if_else_ext(
        &mut self,
        condition: impl Into<Self::Expr> + Clone,
        a: BinomialExtension<impl Into<Self::Expr> + Clone>,
        b: BinomialExtension<impl Into<Self::Expr> + Clone>,
    ) -> BinomialExtension<Self::Expr> {
        BinomialExtension(array::from_fn(|i| {
            self.if_else(condition.clone(), a.0[i].clone(), b.0[i].clone())
        }))
    }
Performs an if else on extension elements.
crates/stark/src/air/builder.rs