anchor.diff:  
   (defun trim-tail (obj seq &key (test #'eql))
     (let len (length seq)
  -	(when (< 0 len)
  +	(when (integer< 0 len)
         (if (funcall test obj (elt seq (integer-1- len)))
   	      (trim-tail obj
   				     (subseq seq 0 (integer-1- len))
  
positive.code:   "Trim start and end of sequence where element is equal to 'obj'."
    (and seq
  	   (if (integer< 0 (length seq))
    		   (trim-tail obj (trim-head obj seq :test test) :test test))
  		   seq))
  
  (define-test "TRIM-HEAD works"
    ((trim-head #\  "  "))
  
negative.code: 		  seq))))
  
  (defun trim-head (obj seq &key (test #'eql))
    (when (integer< 0 (length seq))
      (if (funcall test obj (elt seq 0))
  	    (trim-head obj
  				   (subseq seq 1)
  