How exactly do RGB curves work and interact w/each other in Photoshop?

Question

So I understand how a single curve works:

If you create a curve such that R100 (in) becomes R50 (out), every pixel that has an R value of R100 becomes R50.

Similar deal with the RGB curve:

if you set RGB100 -> RGB50 any pixel that has R or G or B of 100 becomes 50.

So my question is, I've set a RGB curve such that RGB100 -> RGB50 and R100 -> R125, the result is all R100 -> R73. If I reverse that so RGB100 -> RGB125 and R100 -> R50, the result is all R100 -> R66. If I set both RGB100 -> RGB50 and R100 -> R50, the result is all R100 -> R19...

What is the interaction there (mathematically) between the RGB curve and R curve? This is all on the same curves layer.

Answer 1

Hokay, Turns out I was over-thinking the problem (no way!). The answer is values from Curve1 go through Curve2. So on the RGB100 -> RGB50 a R100 value becomes R50, then in the R100 -> R125 curve the R50 value becomes R73.

Voila.