The Comprehensive LaTeX Symbol List

We can just as easily define other barred letters:\def\bbar{{\mathchar’26\mkern-9mu b}}\def\dbar{{\mathchar’26\mkern-12mu d}}(The space after the “mu” is optional but is added for clarity.) \bbar and \dbar define “¯b” and “¯d”, respectively.Note that \dbar requires a greater backward math kern than \bbar; a −9 mu kern would have produced theless-attractive “¯d” glyph.The amsmath package provides \overset and \underset commands for placing one symbol respectivelyabove or below another. For example, \overset{G}{\sim} 7 produces “ G ∼” (sometimes used for “equidecomposablewith respect to G”).Sometimes an ordinary tabular environment can be co-opted into juxtaposing existing symbols into a newsymbol. Consider the following definition of \asterism (“ * ** ”) from a June 2007 post to comp.text.tex byPeter Flynn:\newcommand{\asterism}{\smash{%\raisebox{-.5ex}{%\setlength{\tabcolsep}{-.5pt}%\begin{tabular}{@{}cc@{}}%\multicolumn2c*\\[-2ex]*&*%\end{tabular}}}}Note how the space between columns (\tabcolsep) and rows (\\[. . . ]) is made negative to squeeze theasterisks closer together.There is a TEX primitive called \mathaccent that centers one mathematical symbol atop another. Forexample, one can define \dotcup (“ ·∪”)—the composition of a \cup and a \cdot—as follows:\newcommand{\dotcup}{\ensuremath{\mathaccent\cdot\cup}}The catch is that \mathaccent requires the accent to be a “math character”. That is, it must be a characterin a math font as opposed to a symbol defined in terms of other symbols. See The TEXbook [Knu86a] for moreinformation.Another TEX primitive that is useful for composing symbols is \vcenter. \vcenter is conceptually similarto “\begin{tabular}{l}” in L A TEX but takes a list of vertical material instead of \\-separated rows. Also,it vertically centers the result on the math axis. (Many operators, such as “+” and “−” are also verticallycentered on the math axis.) Enrico Gregorio posted the following symbol definition to comp.text.tex inMarch 2004 in response to a query about an alternate way to denote equivalence:\newcommand*{\threesim}{%\mathrel{\vcenter{\offinterlineskip\hbox{$\sim$}\vskip-.35ex\hbox{$\sim$}\vskip-.35ex\hbox{$\sim$}}}}The \threesim symbol, which vertically centers three \sim (“∼”) symbols with 0.35 x-heights of space betweenthem, is rendered as “∼”. \offinterlineskip is a macro that disables implicit interline spacing. Withoutit, \threesim would have a full line of vertical spacing between each \sim. Because of \vcenter, \threesimaligns properly with other math operators: a ÷ b ∼ c × d.A related L A TEX command, borrowed from Plain TEX, is \ooalign. \ooalign vertically overlaps symbolsand works both within and outside of math mode. Essentially, it creates a single-column tabular environmentwith zero vertical distance between rows. However, because it is based directly on TEX’s \ialign primitive,\ooalign uses TEX’s tabular syntax instead of L A TEX’s (i.e., with \cr as the row terminator instead of \\). Thefollowing example of \ooalign, a macro that defines a standard-state symbol (\stst, “ −◦ ”) as a superscriptedPlimsoll line (\barcirc, “−◦ ”), 8 is due to an October 2007 comp.text.tex post by Donald Arseneau:\makeatletter\providecommand\barcirc{\mathpalette\@barred\circ}\def\@barred#1#2{\ooalign{\hfil$#1-$\hfil\cr\hfil$#1#2$\hfil\cr}}\newcommand\stst{^{\protect\barcirc}}\makeatother7 LATEX’s \stackrel command is similar but is limited to placing a symbol above a binary relation.8 While \barcirc illustrates how to combine symbols using \ooalign, the stmaryrd package’s \minuso command (Table 42 onpage 21) provides a similar glyph (“”) as a single, indivisible symbol.91