%% S. Lurp --- STRETCHY --- MIT License
\def\strty@cd{.5523}
\def\strty@circle#1#2#3{%   x, y, radius
        \strty@pd{#3}{0}{#1}{#2}
    m
        \strty@pd{#3}{\strty@mult\strty@cd{#3}}{#1}{#2}
        \strty@pd{\strty@mult\strty@cd{#3}}{#3}{#1}{#2}
        \strty@pd{0}{#3}{#1}{#2}
    c
        \strty@pd{-\strty@mult\strty@cd{#3}}{#3}{#1}{#2}
        \strty@pd{-#3}{\strty@mult\strty@cd{#3}}{#1}{#2}
        \strty@pd{-#3}{0}{#1}{#2}
    c
        \strty@pd{-#3}{-\strty@mult\strty@cd{#3}}{#1}{#2}
        \strty@pd{-\strty@mult\strty@cd{#3}}{-#3}{#1}{#2}
        \strty@pd{0}{-#3}{#1}{#2}
    c
        \strty@pd{\strty@mult\strty@cd{#3}}{-#3}{#1}{#2}
        \strty@pd{#3}{-\strty@mult\strty@cd{#3}}{#1}{#2}
        \strty@pd{#3}{0}{#1}{#2}
    c
    S
}

\def\strty@extensible#1#2#3#4#5#6#7{%   name, bg code, fg code, symbol, x displacement, y displacement, kern
    \@xp\def\csname #1\endcsname##1{{%
        \setbox0=\hbox{$\strty@repeatit{\numexpr##1-1\relax}{{#4}#7}{{#4}}$}%
        \def\strty@trans####1####2{%
            {\strty@mult{.5}{\strty@nopt{####1\dimexpr\wd0+#5\relax}}}%
            {\strty@nopt{####2\dimexpr#6\relax}}%
        }%
        \rlap{\kern.5\wd0$\vcenter{\pdfliteral{\strty@pttrans\space#2}}$}%
        \rlap{\copy0}%
        \rlap{\kern.5\wd0$\vcenter{\pdfliteral{\strty@pttrans\space#3}}$}%
        \kern\wd0\relax%
    }}%
}%

\def\strty@repeatedsym#1#2#3{%
    \@xp\def\csname #1\endcsname##1{{%
        \strty@repeatit{\numexpr##1-1\relax}{{#2}#3}{{#2}}%
    }}%
}

\def\strty@limitsop@nolim#1#2#3#4#5{% operator, sup, sub, sup kern, sub kern
    \mathop{#1}\nolimits^{\mkern#4#2}_{\mkern#5#3}%
}

\def\strty@limitsop@lim#1#2#3#4#5{% operator, sup, sub, sup kern, sub kern
    \mathop{#1}\limits^{\mkern#4#2}_{\mkern#5#3}%
}

\def\strty@createoplims#1#2#3#4#5{
    \@xp\def\csname \strty@strip#1@nolim\endcsname##1##2##3{%
        \strty@limitsop@nolim{#1{##1}}{##2}{##3}{#2}{#3}
    }%
    \@xp\def\csname \strty@strip#1@lim\endcsname##1##2##3{%
        \strty@limitsop@lim{#1{##1}}{##2}{##3}{#4}{#5}
    }%
}

\strty@repeatedsym{strty@dint@sym}{\displaystyle\int}{\mkern-10mu}
\strty@repeatedsym{strty@tint@sym}{\textstyle\int}{\mkern-7mu}
\strty@createoplims\strty@dint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@tint@sym{0mu}{-7mu}{7mu}{-7mu}

\def\strtyint#1#2#3{%
    \mathchoice%
        {\strty@dint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtyintlimits#1#2#3{%
    \mathchoice%
        {\strty@dint@sym@lim{#1}{#2}{#3}}%
        {\strty@tint@sym@lim{#1}{#2}{#3}}%
        {\strty@tint@sym@lim{#1}{#2}{#3}}%
        {\strty@tint@sym@lim{#1}{#2}{#3}}%
}

\strty@extensible{strty@doint@sym}{}{
    q
    .5 w
    \strty@circle{0pt}{0pt}{1}
    Q
}{\displaystyle\int}{-2pt}{4pt}{\mkern-10mu}

\strty@extensible{strty@toint@sym}{}{
    q
    .5 w
    \strty@circle{0pt}{0pt}{1}
    Q
}{\textstyle\int}{-2pt}{2.3333pt}{\mkern-7mu}

\strty@extensible{strty@dlcaint@sym}{}{
    q
    .5 w
    \strty@circle{0pt}{0pt}{1}
    .3 w
    1 j 1 J
    \strty@p{-1}{0} m
    \strty@pd{-1}{0}{-1pt}{-1.5pt} l
    \strty@p{-1}{0} m
    \strty@pd{-1}{0}{1.5pt}{-1pt} l
    S
    Q
}{\displaystyle\int}{-2pt}{4pt}{\mkern-10mu}

\strty@extensible{strty@tlcaint@sym}{}{
    q
    .5 w
    \strty@circle{0pt}{0pt}{1}
    .3 w
    1 j 1 J
    \strty@p{-1}{0} m
    \strty@pd{-1}{0}{-1pt}{-1.5pt} l
    \strty@p{-1}{0} m
    \strty@pd{-1}{0}{1.5pt}{-1pt} l
    S
    Q
}{\textstyle\int}{-2pt}{2.3333pt}{\mkern-7mu}

\strty@extensible{strty@dsqint@sym}{}{
    q
    .5 w
    1 j 1 J
    \strty@p{-1}{1} m
    \strty@p{1}{1} l
    \strty@p{1}{-1} l
    \strty@p{-1}{-1} l
    s
    Q
}{\displaystyle\int}{-2pt}{4pt}{\mkern-10mu}

\strty@extensible{strty@tsqint@sym}{}{
    q
    .5 w
    1 j 1 J
    \strty@p{-1}{1} m
    \strty@p{1}{1} l
    \strty@p{1}{-1} l
    \strty@p{-1}{-1} l
    s
    Q
}{\textstyle\int}{-2pt}{2.3333pt}{\mkern-7mu}

\strty@extensible{strty@drsqint@sym}{}{
    q
    .5 w
    1 j 1 J
    \strty@pd{-1}{1}{4pt}{0pt} m
    \strty@pd{1}{1}{-4pt}{0pt} l
        \strty@pd{1}{1}{-4pt+\strty@mult\strty@cd{4}pt}{0pt}
        \strty@pd{1}{0}{0pt}{\strty@mult\strty@cd{4}pt}
        \strty@p{1}{0}
    c
        \strty@pd{1}{0}{0pt}{-\strty@mult\strty@cd{4}pt}
        \strty@pd{1}{-1}{-4pt+\strty@mult\strty@cd{4}pt}{0pt}
        \strty@pd{1}{-1}{-4pt}{0pt}
    c
    \strty@pd{-1}{-1}{4pt}{0pt} l
        \strty@pd{-1}{-1}{4pt-\strty@mult\strty@cd{4}pt}{0pt}
        \strty@pd{-1}{0}{0pt}{-\strty@mult\strty@cd{4}pt}
        \strty@p{-1}{0}
    c
        \strty@pd{-1}{0}{0pt}{\strty@mult\strty@cd{4}pt}
        \strty@pd{-1}{1}{4pt-\strty@mult\strty@cd{4}pt}{0pt}
        \strty@pd{-1}{1}{4pt}{0pt}
    c
    s
    Q
}{\displaystyle\int}{-2pt}{4pt}{\mkern-10mu}

\strty@extensible{strty@trsqint@sym}{}{
    q
    .5 w
    1 j 1 J
    \strty@pd{-1}{1}{2.3333pt}{0pt} m
    \strty@pd{1}{1}{-2.3333pt}{0pt} l
        \strty@pd{1}{1}{-2.3333pt+\strty@mult\strty@cd{2.3333}pt}{0pt}
        \strty@pd{1}{0}{0pt}{\strty@mult\strty@cd{2.3333}pt}
        \strty@p{1}{0}
    c
        \strty@pd{1}{0}{0pt}{-\strty@mult\strty@cd{2.3333}pt}
        \strty@pd{1}{-1}{-2.3333pt+\strty@mult\strty@cd{2.3333}pt}{0pt}
        \strty@pd{1}{-1}{-2.3333pt}{0pt}
    c
    \strty@pd{-1}{-1}{2.3333pt}{0pt} l
        \strty@pd{-1}{-1}{2.3333pt-\strty@mult\strty@cd{2.3333}pt}{0pt}
        \strty@pd{-1}{0}{0pt}{-\strty@mult\strty@cd{2.3333}pt}
        \strty@p{-1}{0}
    c
        \strty@pd{-1}{0}{0pt}{\strty@mult\strty@cd{2.3333}pt}
        \strty@pd{-1}{1}{2.3333pt-\strty@mult\strty@cd{2.3333}pt}{0pt}
        \strty@pd{-1}{1}{2.3333pt}{0pt}
    c
    s
    Q
}{\textstyle\int}{-2pt}{2.3333pt}{\mkern-7mu}

\strty@extensible{strty@bthint@sym}{
    q
    1 1 0 rg 1 1 0 RG
    1 j 1 J
    2 w
    \strty@p{-1}{0} m
        \strty@p{-1}{.5}
        \strty@pd{-1}{1}{2pt}{0pt}
        \strty@pd{-1}{1}{4pt}{0pt}
    c
    \strty@pd{1}{1}{-4pt}{0pt} l
        \strty@pd{1}{1}{-2pt}{0pt}
        \strty@p{1}{.5}
        \strty@p{1}{0}
    c
    S
    Q
}{
    q
    1 1 0 rg 1 1 0 RG
    1 j 1 J
    2.1 w
    \strty@p{-1}{0} m
        \strty@p{-1}{-.5}
        \strty@pd{0}{-.75}{-2pt}{0pt}
    v
    \strty@pd{0}{-1.5}{4pt}{0pt} l
    \strty@p{1}{0} m
        \strty@p{1}{-.5}
        \strty@pd{0}{-.75}{2pt}{0pt}
    v
    \strty@pd{0}{-1.5}{-4pt}{0pt} l
    S
    2 w
    \strty@p{-1}{0} m
        \strty@p{-1}{-.5}
        \strty@pd{0}{-.75}{-2pt}{0pt}
    v
    \strty@pd{0}{-1.5}{4pt}{0pt} l
    \strty@p{1}{0} m
        \strty@p{1}{-.5}
        \strty@pd{0}{-.75}{2pt}{0pt}
    v
    \strty@pd{0}{-1.5}{-4pt}{0pt} l
    S
    Q
}{\displaystyle\int}{-2pt}{4pt}{\mkern-10mu}

\strty@extensible{strty@dtriint@sym}{}{
    1 j 1 J
    .5 w
    \strty@p{0}{1} m
    \strty@p{-1}{-1} l
    \strty@p{1}{-1} l
    h
    S
}{\displaystyle\int}{-2pt}{3pt}{\mkern-10mu}

\strty@extensible{strty@ttriint@sym}{}{
    1 j 1 J
    .5 w
    \strty@p{0}{1} m
    \strty@p{-1}{-1} l
    \strty@p{1}{-1} l
    h
    S
}{\textstyle\int}{-2pt}{2pt}{\mkern-7mu}

\strty@createoplims\strty@doint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@toint@sym{0mu}{-7mu}{7mu}{-7mu}
\strty@createoplims\strty@dlcaint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@tlcaint@sym{0mu}{-7mu}{7mu}{-7mu}
\strty@createoplims\strty@dsqint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@tsqint@sym{0mu}{-7mu}{7mu}{-7mu}
\strty@createoplims\strty@drsqint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@trsqint@sym{0mu}{-7mu}{7mu}{-7mu}
\strty@createoplims\strty@dtriint@sym{0mu}{-12mu}{12mu}{-15mu}
\strty@createoplims\strty@ttriint@sym{0mu}{-7mu}{7mu}{-7mu}

\def\strtyoint#1#2#3{%
    \mathchoice%
        {\strty@doint@sym@nolim{#1}{#2}{#3}}%
        {\strty@toint@sym@nolim{#1}{#2}{#3}}%
        {\strty@toint@sym@nolim{#1}{#2}{#3}}%
        {\strty@toint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtyointlimits#1#2#3{%
    \mathchoice%
        {\strty@doint@sym@lim{#1}{#2}{#3}}%
        {\strty@toint@sym@lim{#1}{#2}{#3}}%
        {\strty@toint@sym@lim{#1}{#2}{#3}}%
        {\strty@toint@sym@lim{#1}{#2}{#3}}%
}

\def\strtylcaint#1#2#3{%
    \mathchoice%
        {\strty@dlcaint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtylcaintlimits#1#2#3{%
    \mathchoice%
        {\strty@dlcaint@sym@lim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@lim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@lim{#1}{#2}{#3}}%
        {\strty@tlcaint@sym@lim{#1}{#2}{#3}}%
}

\def\strtysqint#1#2#3{%
    \mathchoice%
        {\strty@dsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtysqintlimits#1#2#3{%
    \mathchoice%
        {\strty@dsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@tsqint@sym@lim{#1}{#2}{#3}}%
}

\def\strtyrsqint#1#2#3{%
    \mathchoice%
        {\strty@drsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@nolim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtyrsqintlimits#1#2#3{%
    \mathchoice%
        {\strty@drsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@lim{#1}{#2}{#3}}%
        {\strty@trsqint@sym@lim{#1}{#2}{#3}}%
}

\def\strtytriint#1#2#3{%
    \mathchoice%
        {\strty@dtriint@sym@nolim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@nolim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@nolim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@nolim{#1}{#2}{#3}}%
}

\def\strtytriintlimits#1#2#3{%
    \mathchoice%
        {\strty@dtriint@sym@lim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@lim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@lim{#1}{#2}{#3}}%
        {\strty@ttriint@sym@lim{#1}{#2}{#3}}%
}

\newbox\strty@pileft
\newbox\strty@piright
\bgroup
\setbox0=\hbox{\vrule width0pt height0pt depth.125pt$\pi$}
\setbox1=\hbox to2.7pt{\copy0\hss}
\setbox2=\hbox to3pt{\hss\copy0}
\pdfxform1
\global\setbox\strty@pileft=\hbox{\pdfrefxform\pdflastxform}
\pdfxform2
\global\setbox\strty@piright=\hbox{\pdfrefxform\pdflastxform}
\egroup

\def\strty@pii#1{%
    \hbox{%
        \strty@setpttrans%
        \copy\strty@pileft%
        \strty@repeatit{#1}{%
            \hbox to1.2pt{\pdfliteral{
                \strty@p{-.1}{4.3} m
                \strty@p{1.3}{4.3} l
                \strty@p{1.3}{3.73} l
                \strty@p{0.725}{3.73} l
                    \strty@p{0.75}{1.5}
                    \strty@p{.8}{1}
                    \strty@p{.9}{.175}
                c
                    \strty@p{.9}{\strty@add{-\strty@mult\strty@cd{.3}}{.175}}
                    \strty@p{\strty@add{\strty@mult\strty@cd{.3}}{.6}}{-.125}
                    \strty@p{.6}{-.125}
                c
                    \strty@p{\strty@add{-\strty@mult\strty@cd{.3}}{.6}}{-.125}
                    \strty@p{.3}{\strty@add{-\strty@mult\strty@cd{.3}}{.175}}
                    \strty@p{.3}{.175}
                c
                    \strty@p{.4}{1}
                    \strty@p{.45}{1.5}
                    \strty@p{0.475}{3.73}
                c
                \strty@p{-.1}{3.73} l
                h
                f
            }\hfil}%
        }%
        \copy\strty@piright%
    }%
}

\def\pii#1{%
    \ifnum#1=1 %
        \tau%
    \else%
        \ifnum#1=2 %
            \pi%
        \else%
            \strty@pii{\numexpr#1-2\relax}%
        \fi%
    \fi%
}