symbols
I need a \leq symbol underlined like the symbol \leqslant (in order to obtain a sort of \lessim version of \leqslant)
That is, with the \sim parallel to the bottom part of \leq (and as well integrated as possible).
Do you know whether such a symbol already exists or is easy to obtain?
You could, of course, use TikZ for this:
The symbol will scale with your font size, since it uses ex to define the path.
\documentclass{article}
\usepackage{tikz}
\begin{document}
\newcommand\shield{%
\tikz [baseline] \draw (0,1.75ex) -- (0,0.75ex) arc [radius=0.75ex, start angle=-180, end angle=0] -- (1.5ex,1.75ex) -- cycle;%
}
A shield: \shield
\end{document}
If you're feeling fancy, you could parametrise it a bit:
\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\begin{document}
\newcommand\shield[1][]{%
\tikzset{
shield width/.store in=\shieldwidth,
shield width=1.5ex,
shield height/.store in=\shieldheight,
shield height=1.75ex
}%
\tikz [baseline,#1] \draw (0,\shieldheight) -- (0,\shieldwidth/2) arc [radius=\shieldwidth/2, start angle=-180, end angle=0] -- (\shieldwidth,\shieldheight) -- cycle;%
}
A shield: \shield
A wide shield: \shield[shield width=2ex]
A tall shield: \shield[shield height=3ex]
\end{document}
There is \providecommand that defines a macro if it is not yet defined. Together with \renewcommand you have your "\extranewcommand":
\providecommand{\foo}{}
\renewcommand{\foo}[1]{bar: #1}
Or you can switch to the plain TeX primitives (other syntax!), e.g.:
\long\def\foo#1{bar: #1}
(\renewcommand and friends without star use \long\def and if the star form is given, \def without \long is used. Also the parameters are specified differently.)
\declarecommandA definition of the "requested" \declarecommand that calls \providecommand and \renewcommand together:
\documentclass{article}
\makeatletter
\newcommand*{\declarecommand}{%
\@star@or@long\declare@command
}
\newcommand*{\declare@command}[1]{%
\provide@command{#1}{}%
% \let#1\@empty % would be more efficient, but without error checking
\renew@command{#1}%
}
\makeatother
\begin{document}
\declarecommand*{\foo}{\typeout{foo 1: \meaning\foo}}
\foo
\declarecommand{\foo}{\typeout{foo 2: \meaning\foo}}
\foo
\declarecommand*{\foo}[1]{\typeout{foo #1: \meaning\foo}}
\foo{3}
\end{document}
Result:
foo 1: macro:->\typeout {foo 1: \meaning \foo }
foo 2: \long macro:->\typeout {foo 2: \meaning \foo }
foo 3: macro:#1->\typeout {foo #1: \meaning \foo }
Best Answer
Here is a solution using
stackengineandgraphicx. Probably you should scale the whole operator down a little bit, but it does what it should be.If you want this as a macro just do
\newcommand\myop{\ensuremath\mathrel{\raisebox{1pt}{\stackunder{$<$}{\rotatebox{-27}{\resizebox{7pt}{2pt}{$\sim$}}}}}}.Update: Use
\boldsymbol{\sim}with a resizebox of 6.5pt instead (as the OP himself/herself suggested) and the output will look nicer.