diff --git a/semantics.rkt b/semantics.rkt
index db972d5..968753a 100644
--- a/semantics.rkt
+++ b/semantics.rkt
@@ -89,7 +89,7 @@
 (define (step state)
   (let ([stack (State-stack state)])
     (match stack
-      [(cons addr _)
+      [(cons addr rstack)
        (step-node state (lookup-node (State-heap state) addr))]
       ['() (error "Invalid state")])))
 
@@ -99,8 +99,33 @@
     [(? integer?) (error "A number cannot be stepped any further!")]
     [(list a _) (update-stack (λ (x) (cons a x)) st)]
     [(list 'define (list name args ...) body)
-     (step-sc st name args body)]))
+     (step-sc st args body)]))
 
-(: step-sc (-> State Name (Listof Name) CoreExpr State))
-(define (step-sc state sc args body)
-  (error "to be implemented"))
+(: step-sc (-> State (Listof Name) CoreExpr State))
+(define (step-sc state arg-names body)
+  (let* ([stack (State-stack state)]
+         [heap (State-heap state)]
+         [new-env : Globals
+                      (for/fold ([globals : Globals (State-globals state)])
+                                ([arg-name : Name arg-names]
+                                 [addr : Addr (if (null? stack)
+                                                   (error "impossible")
+                                                   (cdr stack))])
+                        (update-globals globals arg-name addr))]
+         ;; [new-stack : Stack
+         ;;            (drop stack (add1 (length arg-names)))]
+         )
+    (let-values ([(new-heap addr) (instantiate-body body new-env heap)])
+      (let ([new-stack (cons addr (drop stack (add1 (length arg-names))))])
+        (struct-copy State state [stack new-stack] [heap new-heap])))))
+
+(: instantiate-body (-> CoreExpr Globals Heap (Values Heap Addr)))
+(define (instantiate-body e env heap)
+  (match e
+    [(? integer?) (allocate-node heap e)]
+    [(list f a)
+     (let*-values ([(heap0 addr-f) (instantiate-body f env heap)]
+                   [(heap1 addr-a) (instantiate-body a env heap0)])
+       (allocate-node heap1 (list addr-f addr-a)))]
+    [(? symbol?) (values heap (lookup-globals env e))]
+    [_ (error "unimplemented")]))