Identifying Mystery "R" Symbol

Question

Does anybody know how to typeset the "R" looking symbol on the very left of the image below in latex? I used Detexify and looked through the comprehensive list with no luck.

It appears in a table in Knuth's Art of Computer Programming, Volume 4, page 47. The meaning is given on the right.

Answer 1

Not too bad for a first cut. I used \KnRgap to set aside the field on which I would build the symbol. I then used \stackinset to nest overlays upon the blank field. I started with (i.e., innermost inset) a scaled \supset in the upper right corner of the field, and then added two \rule sticks in the upper left and finally added a rotated \rule stick in the lower right.

To finish it off, I added a point of kern to the left and right of the newly created glyph.

\documentclass{article}
\usepackage{stackengine}
\usepackage{graphicx}
\def\KnRgap{\rule{1.63ex}{0ex}\rule[-.3ex]{0ex}{1.8ex}}
\def\KnR{\kern1pt%
\stackinset{r}{0pt}{b}{0pt}{\rotatebox{53}{\rule{.08ex}{1.3ex}}}{%
\stackinset{l}{0pt}{t}{.02ex}{\rule{.08ex}{1.8ex}}{%
\stackinset{l}{.02ex}{t}{0pt}{\rule{1ex}{.08ex}}{%
\stackinset{r}{0pt}{t}{.02ex}{\scalebox{.76}{$\supset\mkern -2mu$}}{%
\KnRgap%
}}}}\kern1pt%
}
\begin{document}
\KnR~~Right projection; second dictator%
\end{document}

If it is felt that the \supset's "legs" protrude too far leftward, an alternative can be had by importing a single symbol from the mathabx package in its place:

\documentclass{article}
\DeclareFontFamily{U}{matha}{\hyphenchar\font45}
\DeclareFontShape{U}{matha}{m}{n}{
      <5> <6> <7> <8> <9> <10> gen * matha
      <10.95> matha10 <12> <14.4> <17.28> <20.74> <24.88> matha12
      }{}
\DeclareSymbolFont{matha}{U}{matha}{m}{n}
\DeclareMathSymbol{\varcup}{3}{matha}{"59}

\usepackage{stackengine}
\usepackage{graphicx}
\def\KnRgap{\rule{1.45ex}{0ex}\rule[-.3ex]{0ex}{1.8ex}}
\def\KnR{\kern1pt%
\stackinset{r}{0pt}{b}{0pt}{\rotatebox{45}{\rule{.08ex}{1.14ex}}}{%
\stackinset{l}{0pt}{t}{.02ex}{\rule{.08ex}{1.8ex}}{%
\stackinset{l}{.02ex}{t}{0.0pt}{\rule{.7ex}{.08ex}}{%
\stackinset{r}{0pt}{t}{0.0ex}{\scalebox{.81}{%
  \rotatebox{90}{$\varcup\mkern -2mu$}}}{%
\KnRgap%
}}}}\kern1pt%
}
\begin{document}
\KnR~~Right projection; second dictator%
\end{document}