# What does this notation $p(s', r \mid s, a)$ mean in reinforcement learning?

I was reading a book on reinforcement learning, and came across the following notation:

Possibly stupid question, but I cant seem to google how to read this. Is it

A) Probability of (s' and r) GIVEN (s and a)

B) Probability of s' and (r GIVEN s) and a?

I know this may seem like a stupid question, but I really could not find any guide on how to read this triple notation online. Thank you for your time!

It is the probability that the state ($$S_t$$) and reward ($$R_t$$) at time $$t$$ are respectively equal to some $$s'$$ and $$r$$, given that the state ($$S_{t-1}$$) and the action taken from that state ($$A_{t-1}$$) at time $$t-1$$ are respectively equal to some $$s$$ and $$a$$.