def is_mag_data(mdat):
if not pimms.is_map(mdat): return False<EOL>for k in ['<STR_LIT>', '<STR_LIT>', '<STR_LIT>', '<STR_LIT>', '<STR_LIT>',<EOL>'<STR_LIT>', '<STR_LIT>', '<STR_LIT>', '<STR_LIT>']:<EOL><INDENT>if k not in mdat: return False<EOL><DEDENT>return True<EOL>
is_mag_data(dat) yields True if the given data is a valid set of magnification data and False
  otherwise.

Note that this does not return True for all valid return values of the mag_data() function:
specifically, if the mag_data() function yields a list of mag-data maps or a lazy-map of the
mag-data maps split out by visual area, then this will return False. This function only returns
True for a map of mag data itself.