fn var_evaluate<F: FieldWitness>(
v: &Variable<Column>,
evals: &ProofEvaluations<PointEvaluations<F>>,
) -> Result<F, ExprError<Column>>
fn var_evaluate<F: FieldWitness>(
v: &Variable<Column>,
evals: &ProofEvaluations<PointEvaluations<F>>,
) -> Result<F, ExprError<Column>>