Checks whether an object has a specific component or not. If the first argument is a string, the object with the specified name is regarded as a list object.
execfile executes all commands contained in the specified file. Files are only seeked in the current directory. If necessary the suffix '.xpl' is appended. If both versions, i.e. with and without suffix, are available the file with suffix will be processed.
free removes global objects. It is convenient to delete big objects which consume a lot of memory. If free is invoked without arguments all objects are deleted.