債権の利子計算

現在Vasicekの論文を読んでいます。彼の導出に分からない事が多いです。 The objective of the paper seems to be to provide formulas to determine the present value of bonds and their term interest rates, given a maturity date.
One point I do not understand is his frequent citation of the Ito rules and theorems.
Another point is how he obtains an equation for P (the current price of a bond) in terms of the expectation of an exponential function of integrals. He claims that:
E(t)(P(s,s)V(s)-P(t,s)V(t))=0 enables the P(t,s) expression to be derived, but I am unsure how. It seems that he defines V(s) to be the exponential which P is the expectation of. Unless P(s,s) equals one and E(P(t,s)V(t))=P(t,s), the derivation does not seem to hold. P(s,s) does equal 1. I am not sure what E(t) means in this case, as, if it were the expectation of the output for all possible t values, then P could not be a function of t. Perhaps it means expectation for function of s given a certain t value, but then P could not be a function of s.
At any rate, the point is that a quadratic differential equation for P can be converted to a solution involving a definite integral.