I assume package amsmath
is loaded (e.g. needed for \iff
).
\implies
, \impliedby
, and \iff
adds a surrounding space of \;
, that is space of
the amount \thickmuskip
. Macro \HalfThickmuskip
uses the half of \;
.
\implies
, \impliedby
are composed of the arrow with the equals sign.
Macro \HalfRelbar
uses the same equals sign, but the width is scaled by factor 0.5.
\joinrel
fixes the side bearings (horizontal space surrounding the glyph shape) and is adjusted to the smaller side bearings of the scaled equals sign in macro \PartJoinrel
.
The case of \iff
is different, because it is composed by the two arrows that cannot be scaled without affecting the arrow tips. Here the half width of the equals sign is subtracted.
As assumed, package accsupp
is used to get a better Unicode representation of the
glyph constructs.
\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{graphics}
\usepackage{accsupp}
\makeatletter
\newcommand*{\HalfRelbar}{%
\mathrel{%
\mathpalette\MathResizeHalfWidth=%
}%
}
\newcommand*{\MathResizeHalfWidth}[2]{%
\scalebox{.5}[1]{$\m@th#1#2$}%
}
\newcommand*{\HalfThickmuskip}{%
\mskip.5\muexpr\thickmuskip\relax
}
\newcommand*{\NegHalfEquals}{%
\mathrel{%
\mathpalette\@NegHalfEquals=%
}%
}
\newcommand*{\@NegHalfEquals}[2]{%
\setbox0=\hbox{$\m@th#1#2$}%
\kern-.5\wd0 %
}
\newcommand*{\PartJoinrel}{%
\mathrel{\mkern-2.25mu}% -3mu/2 -1.5mu/2
}
\newcommand*{\Implies}{%
\DOTSB
\protect\HalfThickmuskip
\protect\BeginAccSupp{method=hex,unicode,ActualText=21D2}%
\protect\HalfRelbar
\protect\PartJoinrel
\protect\Rightarrow
\protect\EndAccSupp{}%
\protect\HalfThickmuskip
}
\newcommand*{\Impliedby}{%
\DOTSB
\protect\HalfThickmuskip
\protect\BeginAccSupp{method=hex,unicode,ActualText=21D0}%
\protect\Leftarrow
\protect\PartJoinrel
\protect\HalfRelbar
\protect\EndAccSupp{}%
\protect\HalfThickmuskip
}
\newcommand*{\Iff}{%
\DOTSB
\protect\HalfThickmuskip
\protect\BeginAccSupp{method=hex,unicode,ActualText=21D4}%
\protect\Leftarrow
\protect\joinrel
\protect\NegHalfEquals
\protect\Rightarrow
\protect\EndAccSupp{}%
\protect\HalfThickmuskip
}
\makeatother
\begin{document}
\begin{gather*}
a \implies b_{a \implies b} \\
a \Implies b_{a \Implies b} \\
a \Rightarrow b_{a \Rightarrow b} \\
c \impliedby d_{c \impliedby d} \\
c \Impliedby d_{c \Impliedby d} \\
c \Leftarrow d_{c \Leftarrow d} \\
e \iff f_{e \iff f}\\
e \Iff f_{e \Iff f} \\
e \Leftrightarrow f_{e \Leftrightarrow f} \\
\end{gather*}
\end{document}
