Mathematics uses symbols to represent mathematical relationships. The “similar” symbol represents a relationship between two elements where they are related, but not equal.
The following is an article by Jieyi describing the various symbols used to indicate that something is similar to something else.
The similarity command can be confusing since several commands produce different results. However, if you understand the differences, you’ll know which one to use in any situation.
Core similarity commands
Several TeX packages include a wide range of symbols that help to express the relationship between elements. While these aren’t all the symbols that exist, each has its own specific meaning. They are:
\sim (similar to)
\simeq (similar or equal to; the field determines the convention)
\cong (congruent to)
\approx (approximately equal)
\equiv (identical to)
\propto (proportional to)
The following table contains these commands and their usual meanings. Many core relations are available in standard LaTeX. Less common variants such as \lesssim, \gtrsim, \eqslantless, and \eqslantgtr are provided by amssymb; package requirements should be checked command by command.
The core similarity commands
Command
Meaning
Notes
\sim
~ Similar
This requires no extra package.
\cong
Congruent to
This requires no extra package.
\approx
Approximately equal to
This requires no extra package.
\simeq
Similar or equal to
No extra package in standard LaTeX.
\propto
Proportional to
This requires no extra package.
\equiv
Identical to
This requires no extra package.
\lesssim
Less than or similar to
Requires the amssymb package.
\gtrsim
Greater than or similar to
Requires the amssymb package.
\eqslantless
Equal to or less than
Requires the amssymb package.
\eqslantgtr
Equal to or greater than
Requires the amssymb package.
Inequality commands
A number of other commands provide inequalities involving the ~ symbol.
Command
Meaning
Notes
\leq
Less than or equal to
No package required.
\geq
Greater than or equal to
No package required.
\ll
Much less than
No package required.
\gg
Much greater than
No package required.
\prec
Precedes
No package required.
\succ
Succeeds
No package required.
\preceq
Precedes or equals
No package required.
\succeq
Succeeds or equals
No package required.
\subset
Is a subset of
No package required.
\supset
Is a superset of
No package required.
\subseteq
Is a subset of or equals
No package required.
\supseteq
Is a superset of or equals
No package required.
The basic inequalities above are available in standard LaTeX; the less common combinations below require amssymb.
Other inequality commands
You can also create combinations of symbols like this:
\lesseqqgtr
Less than or equal to or greater than
Requires the amssymb package.
\geseqqless
Greater than or equal to or less than
Requires the amssymb package.
\lessgtr
Less than or greater than
Requires the amssymb package.
\gtrless
Greater than or less than
Requires the amssymb package.
Relational symbols
The relational symbols below are ordering or relation operators. The listed core commands do not all require an extra package; check a command's note instead of applying one package rule to the entire section.
Command
Meaning
Notes
\perp
Perpendicular
No package required.
\mid
Vertical line
No package required.
\parallel
Parallel
No package required.
\Join
Join
No package required.
\in
Member of
No package required.
\notin
Not member of
No package required.
\ni
Inverse membership
No package required.
\subsetneq
Proper subset
No package required.
\supsetneq
Proper superset
No package required.
The relational commands can be combined, as well. For example:
\subsetneq
Proper subset
No package required.
\subseteqq
Subset or equal
No package required.
\supseteqq
Superset or equal
No package required.
\sqsubset
Square subset
No package required.
\sqsupset
Square superset
No package required.
There’s also the option to make these characters appear in boldface type or italics. Here are those commands, as well.
Command
Meaning
Notes
\mathbf{~}
Bold
No package required.
\mathit{~}
Italic
No package required.
However, there may be times when you’re unsure what the command is, especially when dealing with a lot of math symbols. In those cases, you can always use Detexify, which allows you to draw the symbol that you want. Then, it will tell you what LaTeX command produces the symbol you’ve drawn.