Basic Probability Rule

#1
Hello friends,
Can anyone please give me any authentic resource (book/ literature review article/ any other useful documents ) of this rule. Also can you please let me know what this rule is called.

It doesn't necessarily have to be a chain rule. You can also consider,
P(A + B) = 1 - [ ( 1 - P(A)) * ( 1 - P(B)) ]

Thank you so much in advance.
Probability rule.JPG
 
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