(defun make-term-variable (ring nvars pos
				&optional
				(power 1)
				(coeff (funcall (ring-unit ring)))
				&aux
				(monom (make-monom nvars :initial-element 0)))
  (declare (fixnum nvars pos power))
  (incf (monom-elt monom pos) power)
  (make-term monom coeff))

(defstruct (term
	    (:constructor make-term (monom coeff))
	    ;;(:constructor make-term-variable)
	    ;;(:type list)
	    )
  (monom (make-monom 0) :type monom)
  (coeff nil))

(defun term-sugar (term)
  (monom-sugar (term-monom term)))

(defun termlist-sugar (p &aux (sugar -1))
  (declare (fixnum sugar))
  (dolist (term p sugar)
    (setf sugar (max sugar (term-sugar term)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Additional structure operations on a list of terms
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun termlist-contract (p &optional (k 1))
  "Eliminate first K variables from a polynomial P."
  (mapcar #'(lambda (term) (make-term (monom-contract k (term-monom term))
				      (term-coeff term)))
	  p))

(defun termlist-extend (p &optional (m (make-monom 1 :initial-element 0)))
  "Extend every monomial in a polynomial P by inserting at the
beginning of every monomial the list of powers M."
  (mapcar #'(lambda (term) (make-term (monom-append m (term-monom term))
				      (term-coeff term)))
	  p))

(defun termlist-add-variables (p n)
  "Add N variables to a polynomial P by inserting zero powers
at the beginning of each monomial."
  (declare (fixnum n))
  (mapcar #'(lambda (term)
	      (make-term (monom-append (make-monom n :initial-element 0)
				       (term-monom term))
			 (term-coeff term)))
	  p))