\starttext

% \defineproperty[old][layer]
% \defineproperty[new][layer]

% \def\ShowBothPages#1#2%
%   {\startTEXpage
%      \startoverlay
%        {\startproperty[old]\externalfigure[#1]\stopproperty} % [page=1]
%        {\startproperty[new]\externalfigure[#2]\stopproperty}
%      \stopoverlay
%    \stopTEXpage}

% \ShowBothPages{layer-001-1.pdf}{layer-001-2.pdf}

\stoptext
