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