System variable
%% is the output expression (e.g., %o1, %o2, %o3, ...)
most recently computed by Maxima,
whether or not it was displayed.
% is recognized by batch and load.
In a file processed by batch,
% has the same meaning as at the interactive prompt.
In a file processed by load,
% is bound to the output expression most recently computed at the interactive prompt
or in a batch file;
% is not bound to output expressions in the file being processed.