(formula explained using LATEX code)

Pg 242 Topic 5.6.2: Futures contract

Risk-neutral pricing of a zero-coupon bond is given by the below formulae:

[math]B(t,T) \, = \,\frac{1}{D(t)}. \tilde E~[D(T)\mid F(t)], 0\,\leq \,t\,\leq\,T\,\leq\,\bar T[/math]

I understand here the interest rates are not constant, but is either deterministic or stochastic.

The interest rate path of D(t), it is either a subset or adaptable from the path of D(T).

If my understanding is correct, why cannot we nullify the common path for the period [0,t].

If we take D(t) inside the E-tilda then the following will be the steps:

[math]B(t,T) \, = \, \tilde E [ exp\{ -\int_{0}^{t} R(u)\,du+ \int_{0}^{T} R(u)\,du\}\mid F(t)][/math][math]B(t,T) \, = \, \tilde E [ exp\{ \int_{t}^{T} R(u)\,du\} \mid F(t)][/math]

Since it is now full expectation, or the period [t,T] is not dependent on Filtration (t), we can write the above as

[math]B(t,T) \, = \, \tilde E [ exp\{ \int_{t}^{T} R(u)\,du\}][/math]

If I turn to page Page 218 Topic 5.2.4 Pricing under the Risk-Neutral measure.

I compare Equation 5.2.30 and 5.2.31 In Equation 5.2.31, the D(t) is taken inside E-tilda

[math]V(T)\,=\, \tilde E [exp\{ − \int_{t}^{T} R(u)\,du \}.V(T) \mid F(t)][/math]

My doubt is, if it could be taken inside E-tilda in Equation 5.2.31 why I cannot consider D(t) in E-tilda in Topic 5.6.2 for Zero-coupon bond.

Kindly if anyone can help clarify this difference in approach.