Linear APR model

The linear APR model is a pricing model for a Principal Token quoted in underlying. It assumes that the price of the PT is a unit of underlying discounted by a non-compounded implied rate that stays constant during the term. More specifically, is assumes

$$P(t,T) =\text{PT.previewRedeem(1)}\frac{1}{1+r(T-t)}$$

where $\text{previewRedeem(1)}$ gives the redemption rate of the PT, $T$ is the maturity timestamp, while $t$ is the current timestamp.