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Sequential superposition of plane waves. en April made in Mathematica with the following sloppy but effective code Doajj Plot Cosx Cos jj Pi Pi PlotRange Axes True False Ticks False jj Doajj Plot Cosx jj Cos jj Cos Pi Pi PlotRange Axes True False Ticks False jj Doajj Plot Cosx Cos Cos jj Pi Pi PlotRange