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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