Is this a typo on this Bayes' theoreom blog?

Question

on this site https://diego.assencio.com/?index=b30e25e3b6a86586342729a19cfaf299 where it says "In other words..as long as we know P(A|B), P(A|B') and P(B)=1−P(B')" should that read "In other words..as long as we know P(A|B), P(A|B') and P(B)"?

Answer 1

I don't think it's a typo. It's just a more concise, though slightly ungrammatical, way of saying:

... as long as we know $P(A \mid B)$, $P(A \mid B^c)$ and $P(B)$. Keep in mind that $P(B)=1-P(B^c)$.

I think they wanted to mention this in case the reader is worried that the formula also contains $P(B^c)$. But if you know $P(B)$ then you also know $P(B^c)$.