The \footnote command places a numbered footnote at the bottom of the current page containing the contents of the argument, text. The optional argument, num, is used to change the default footnote number. This command can only be used in outer paragraph mode.
If num is not specified, the footnote counter is incremented and its value is used.
Note that num is specified as a positive integer even if the footnote counter has been set to use letters or roman numerals.