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How to make TikZ cancel "overlay aware" in Beamer?

Code taken from Cancel maths expression with a down arrow

documentclass{beamer}

usepackage{tikz}

tikzset{

main node/.style={inner sep=0,outer sep=0},

label node/.style={inner sep=0,outer ysep=.2em,outer xsep=.4em,font=scriptsize,overlay},

strike out/.style={shorten <=-.2em,shorten >=-.5em,overlay},

strikee out/.style={shorten <=-.2em,shorten >=-.2em,overlay}

}

%

newcommand{cancel}[2]{tikz[baseline=(N.base)]{

  node[main node](N){$#2$};

  draw[strikee out,#1]  (N.south west) -- (N.north east);

}}

%

begin{document}

%

begin{frame}

begin{align*}

a &= frac{b}{c}\

&= frac{b}{b cdot d}\

end{align*}

end{frame}

%

%

begin{frame}

begin{align*}

a &= frac{b}{c}\

&= frac{cancel[red]{b}}{cancel[red]{b} cdot d}\

end{align*}

end{frame}

%

end{document}

I take that you want to cancel only on certain frames. If so, you might be looking for the overlay-beamer-styles library. You only need to add visible on=<...> for the cancel line being visible on the frames ....

documentclass{beamer}

usepackage{tikz}

usetikzlibrary{overlay-beamer-styles}

tikzset{

main node/.style={inner sep=0,outer sep=0},

label node/.style={inner sep=0,outer ysep=.2em,outer xsep=.4em,font=scriptsize,overlay},

strike out/.style={shorten <=-.2em,shorten >=-.5em,overlay},

strikee out/.style={shorten <=-.2em,shorten >=-.2em,overlay}

}

%

newcommand{Cancel}[2]{tikz[baseline=(N.base)]{

  node[main node](N){$#2$};

  draw[strikee out,#1]  (N.south west) -- (N.north east);

}}

%

begin{document}

%

%

begin{frame}

begin{align*}

a &= frac{b}{c}\

&= frac{Cancel[red,visible on=<2>]{b}}{Cancel[red,visible on=<2>]{b} cdot d}\

end{align*}

end{frame}

%

end{document}