who is Thomas Bayes
P(A|B)= P(B|A) * P(A) / P(B)
the theorem expresses how a degree of belief (I am Covid positive)
expressed as a probability,
should rationally change to account for
the availability of related evidence
where A|B are events and P(B) not 0 and P(B) not 0.
P(A|B) are P(A|B) is a conditional probabilities:
the likelihood of event A occurring is conditional on B is true.
P(B|A)} is also a conditional probability:
the likelihood of event B occurring given A is true.
P(A) and P(B) are the probabilities of observing A and B respectively;
are known as marginal probabilities.
A and B must be different events.
https://www.britannica.com/biography/Thomas-Bayes