What does the mathematical expression 9 ∉ T mean?

1 Answer
sente · Room 204
Dec 14, 2015

9 !in T means that 9 is not an element of the set T.

Explanation:

The symbol !in is used with a set S and a potential element a of S to mean

a !in S

if and only if a is not an element of S. Some people like to say that a "does not belong" to set T.

(compare to in which implies an element is in a set)

Thus 9 !in T means that 9 is not an element of the set T

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