butfirst  -- Operation, one input.  Abbreviation: bf
     The input may be any non-empty Logo object.  If the input is  a  list,
     the output is a list equal to the input list with the first member re-
     moved.  (If the input list has only one member, the output is the emp-
     ty  list, a list of zero members.)  If the input is a word, the output
     is a word equal to the input word with the first letter removed.   (If
     the  input is a single-letter word, the output is the empty word.)  If
     the input is empty, an error results.
