Function view_over 

fn view_over<'a, R: Scalar>(
    under_solve: ResolvedCurve<'a, R>,
    stores: &Stores<'a, R>,
) -> Result<PricingView<'a, R>, CalibrationError>

The view a rung is valued in, with under_solve in the role the ladder’s form gives it: the discount curve for a self-discounting solve, the projection curve over a fixed discount otherwise.

Shared by the Newton step and the Jacobian assembly so the two cannot drift: a Jacobian built in a view the solve did not use would describe a different calibration than the one that produced the curve.