1. In the light transport equation(rendering equation), the bsdf describes the flow from light to eye. Am I correct that, under all transport cases(light transport or importance transport), if I used the original bsdf function then the argument ordering in the function is always w(towards light)->w(towards eye) ? So if I always use wi for the direction pointing towards light, wo for direction pointing towards eye and use the bsdf(wi->wo), then I don't need the adjoint bsdf? The adjoint bsdf is only used to correct the flow into the direction from light to eye and make the two transport equations identical, when wi is used conventionally as the direction being sampled ?
2. I'm quite confused with the adjoint bsdf for refraction, Veach derived that there's no eta scaling in the adjoint bsdf, and gave the intuition that the light particles carry power, not radiance. Does this mean that there is no scaling at all in a particle tracing implementation? Then how can the result be the same as path tracing? For example, an area light is placed under the water, and a lens above the water, there would be a scaling factor between the air-water interface in path tracing but not in particle tracing? Aren't the results of two methods different?
3. This is a question about MIS in bidirectional path tracing.
When I use the russian roulette to determine subpath lengths, the probability for sampling next vertex should be multiplied by the continue probability(page 310). When computing MIS weights, it's required to compute the probability of sampling vertex in inverse direction(page 306, the numerator of 10.9), then should this probability consider the russian roulette continue probability (multiply by what)?
Sorry for my poor English, and for my probably misunderstanding of the materials. Looking forward to your help. Thanks~

Jun