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For example, saying that something is specifically not in the domain of integers (not sure how to write the 'N' symbol).

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    $\begingroup$ Like $a\notin\Bbb N$? $\endgroup$ Apr 19, 2019 at 14:42
  • $\begingroup$ To produce $\mathbb{N}$, type $\mathbb{N}$. This tutorial explains how to typeset mathematics on this site. $\endgroup$ Apr 19, 2019 at 14:44
  • $\begingroup$ Thanks for the help. I have realised I was being silly. I was thinking of something else and so I skipped over the fact that 'a∉N' is what I am looking for - I can't explain why, I am just silly. $\endgroup$ Apr 19, 2019 at 14:51
  • $\begingroup$ It may be useful to remember that we can use something like $a \in \mathbb{Q}\backslash \mathbb{Z}$ if we want a non-integer rational number. $\endgroup$ Apr 19, 2019 at 16:05

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Traditionally, the integers are denoted by $\mathbb{Z}$ which in Latex is written $\mathbb{Z}$. By enclosing Z in \mathbb{}, you are telling Latex to write Z in the math blackboard bold font, which is the standard font for sets of numbers. The natural numbers are denoted by $\mathbb{N}$, i.e. $\mathbb{N}$.

Mathematicians use an epsilon symbol to mean "is an element of." That is, $x \in \mathbb{Z}$ is read as "$x$ is an element of $\mathbb{Z}$." The Latex command for this epsilon is \in.

You want to say that something is not in the integers. To negate a statement, mathematicians often put a slash through a symbol. The statement $x \not\in \mathbb{Z}$ is read as "$x$ is not an element of $\mathbb{Z}$." The Latex command for this is $x \not\in \mathbb{Z}$. In general, prefixing a symbol with '\not' in Latex will put a slash through it.

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