What does the subset with slash symbol mean?

Question

What does the following mean:

$\nsubseteq$

I cant find any definition for it?

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Previous editor's note: I replaced a linked image with the $\nsubseteq$ symbol to make the question self-contained. I am pointing this out here to avoid comments/questions such as, "You don't know what it means but you know how to write it in $\mathrm\TeX$?"

Answer 1

Quite simply, $\not\subseteq$ means "not subset of." Hence, $A\not\subseteq B$ means that $A$ is not a subset of $B$.

All the more to make this clear, that symbol is easily typeset with \not\subseteq.

Answer 2

Is not a subset of. If $A \nsubseteq B$, it means that $A$ is not a subset of $B$.

Answer 3

If A ⊈ B, then no member of A is a member of B.

The symbol '⊈' represent the negation of the relation of improper inclusion, '⊆'. A ⊆ B if and only if all member of A is a member of B or if A = B.

Must be distinguished from the negation of the proper inclusion '⊂'. 'A ⊂ B' says that all member of A are members of B, but is not the case that A = B.

Thereby, for example, A ⊆ A, but is not the case that A ⊂ A.