diff --git a/decons.lisp b/decons.lisp
index 0018d32..7af7673 100644
--- a/decons.lisp
+++ b/decons.lisp
@@ -6,8 +6,8 @@
   (:export #:+pi+ #:area #:circle
            #:absv #:double #:remainder
            #:scalar-p #:tensor #:at
-           #:rapply #:rreduce
-           #:combine #:cost #:l2-loss
+           #:rapply #:rreduce #:radd #:rmul #:rsub #:rdiv
+           #:combine #:default-deviation #:l2-loss
            #:line
            #:lgx
            ))
@@ -88,6 +88,11 @@
   (:method (op (v list) &key (initial-value 0)) 
     (rreduce op v :initial-value initial-value)))
 
+(defun radd (a b) (rapply #'+ a b))
+(defun rmul (a b) (rapply #'* a b))
+(defun rsub (a b) (rapply #'- a b))
+(defun rdiv (a b) (rapply #'/ a b))
+
 ;;;; combine
 
 (defun combine (l1 l2)
@@ -97,22 +102,23 @@
   (:method (a b) (list a b))
   (:method (a (b list)) (cons a b)))
 
-;;;; cost / loss calculation
-
-(defun cost (measured calculated)
-  (reduce #'+ 
-          (mapcar (lambda (p) (sqr (apply #'- p))) 
-                  (combine measured calculated))))
-
-(defun l2-loss (target &key (norm #'sqr))
-  (lambda (dataset)
-    (lambda (theta)
-      (let ((calculated (funcall (funcall target (car dataset)) theta)))
-        (reduce #'+ (mapcar (lambda (p) (funcall norm (apply #'- p)))
-                            (combine (cadr dataset) calculated)))))))
+;;;; loss calculation
 
 (defun sqr (x) (* x x))
 
+(defun sum (data) (reduce #'+ data))
+
+(defun default-deviation (observed calculated &key (norm #'sqr))
+  (sum (mapcar (lambda (p) (funcall norm (apply #'- p))) 
+               (combine observed calculated))))
+
+(defun l2-loss (target &key (deviation #'default-deviation))
+  (lambda (dataset) ; expectant function
+    (lambda (theta) ; objective function
+      (let* ((objective (funcall target (car dataset)))
+             (calculated (funcall objective theta)))
+        (funcall deviation (cadr dataset) calculated)))))
+
 ;;;; logging (printing) functions for debugging purposes
 
 (defun lgx (op)
@@ -121,7 +127,7 @@
     (format t "~&(~a ~a) = ~a~%" op args r)
     r)))
 
-;;;; parameterized functions
+;;;; parameterized target functions
 
 (defun line (x)
-  #'(lambda (theta) (rapply #'+ (cadr theta) (rapply #'* (car theta) x))))
+  #'(lambda (theta) (radd (cadr theta) (rmul (car theta) x))))
diff --git a/test-decons.lisp b/test-decons.lisp
index 6fe557a..665176a 100644
--- a/test-decons.lisp
+++ b/test-decons.lisp
@@ -40,10 +40,10 @@
 (deftest test-rapply ()
   (== (decons:rapply #'1+ 7) 8)
   (== (decons:rapply #'1+ '(2 3)) '(3 4))
-  (== (decons:rapply #'+ 2 3) 5)
-  (== (decons:rapply #'+ 3 '(4 5)) '(7 8))
-  (== (decons:rapply #'+ '(2 3) '(4 5)) '((6 7) (7 8))) ; not '(6 8)
-  (== (decons:rapply #'- '(6 7) '(4 5)) '((2 3) (1 2))) 
+  (== (decons:radd 2 3) 5)
+  (== (decons:radd 3 '(4 5)) '(7 8))
+  (== (decons:radd '(2 3) '(4 5)) '((6 7) (7 8))) ; not '(6 8)
+  (== (decons:rsub '(6 7) '(4 5)) '((2 3) (1 2))) 
 )
 
 (deftest test-rreduce ()
@@ -61,7 +61,8 @@
     (setf ps1 (decons:line (car ds1)))
     (== (funcall ps1 '(0.5 2.0)) '(3.0 2.5 4.0 3.5))
     (== (funcall ps1 '(1.0 0.0)) '(2.0 1.0 4.0 3.0))
-    (== (decons:cost (cadr ds1) (funcall ps1 '(1.0 0.0))) 0.20999993) ;0.899999861)
+    (== (decons:default-deviation (cadr ds1) (funcall ps1 '(1.0 0.0))) 
+        0.20999993) ;0.899999861)
     (setf objective (funcall (decons:l2-loss #'decons:line) ds1))
     (== (funcall objective '(0.0 0.0)) 33.21)
 ))