Wald Equation for Discounted Sums. Suppose that ξ0, ξ1,... are costs incurred at discrete times and they are i.i.d. with mean μ. Consider the discounted cost process  is a discount Brownian Motion...

Wald Equation for Discounted Sums. Suppose that ξ0, ξ1,... are costs incurred at discrete times and they are i.i.d. with mean μ. Consider the discounted cost processis a discount Brownian Motion factor. Suppose that τ is a stopping time of the process ξn such that E[τ] <><>