Symbols:General

$$\not=, \not>, \not<, \not\geq, \not\leq, \not\in, \not\exists, \not\subseteq, \not\subset, \not\supseteq, \not\supset$$

"Negation". The above symbols all mean the opposite of the non struck through version of the symbol. For example, $$x \not\in S$$ means that $$x$$ is not an element of $$S$$. The slash through a symbol ($$/$$ ) can be used to reverse the meaning of essentially any mathematical symbol (especially relations), although it is used most frequently with those listed above. Note that $$\not\subsetneq$$ and $$\not\supsetneq$$ can be confusing due to the strike through of the symbol as a whole and the strike through of the equivalence bar on the bottom, and hence should likely be avoided.

See Arithmetic and Algebra and Set Operations and Relations for the definitions of the symbols above.