diff --git a/ods/data/Makefile.am b/ods/data/Makefile.am
deleted file mode 100644
index e324dbe..0000000
--- a/ods/data/Makefile.am
+++ /dev/null
@@ -1,18 +0,0 @@
-pkgdata_DATA = corpus.txt ods-cpp/main.cpp ods-cpp.pdf
-
-corpus.txt: corpus.txt.gz
-	gzip -d -k $@.gz
-
-ods-cpp/main.cpp: ods-cpp.tgz
-	tar xzf ods-cpp.tgz
-
-ODS_SAMPLE_CODE_URL :=		http://opendatastructures.org/ods-cpp.tgz
-ods-cpp.tgz:
-	if command -v curl 2>&1 > /dev/null ; then curl -L -O $(ODS_SAMPLE_CODE_URL) ; \
-	elif command -v curl 2>&1 > /dev/null ; then wget $(ODS_SAMPLE_CODE_URL) ; fi
-
-ODS_PDF_URL :=			http://opendatastructures.org/ods-cpp.pdf
-ods-cpp.pdf:
-	if command -v curl 2>&1 > /dev/null ; then curl -L -O $(ODS_PDF_URL) ; \
-	elif command -v curl 2>&1 > /dev/null ; then wget $(ODS_PDF_URL) ; fi
-
diff --git a/ods/notes/chapter2.txt b/ods/notes/chapter2.txt
index 9ef8889..6152937 100644
--- a/ods/notes/chapter2.txt
+++ b/ods/notes/chapter2.txt
@@ -19,3 +19,15 @@ resizing isn't too bad.
 * Uses backing array *a*.
 * Typically, the array will be larger than necessary, so an element *n* is
   used to track the actual number of elements stored in the stack.
+* Add and remove requires shifting all the elements after i (O(n - i)
+  complexity), ignoring potential calls to resize
+* Resizing is triggered when we run out of room in an add or when a remove
+  brings us to the point where the array is more than 3n elements
+* Resizing creates a new array of size 2n and copies all the elements over;
+  this then has complexity O(n).
+* The analysis of add and remove didn't consider cost of resize.
+* An amortised analysis is done instead that considers the cost of all calls
+  to add and remove, given a sequence of *m* calls to either.
+* Lemma: if an empty ArrayStack is created and any sequence of *m* >= 1 calls
+  to add and remove are performed, the total time spent in calls to resize is 
+  O(m).
diff --git a/ods/src/array_test.cc b/ods/src/array_test.cc
index ef3c8c8..aaefb9c 100644
--- a/ods/src/array_test.cc
+++ b/ods/src/array_test.cc
@@ -23,4 +23,11 @@ main(void)
 	cout << "as[1] " << as.get(1) << endl;
 	as.remove(0);
 	cout << "as[0] " << as.get(0) << endl;
+
+	cout << "size: " << as.size() << ", cap: " << as.cap() << endl;
+	as.add(0, 47);
+	as.add(0, 11);
+	as.add(0, 17);
+	as.add(0, 1);
+	cout << "size: " << as.size() << ", cap: " << as.cap() << endl;
 }
diff --git a/ods/src/ods/array_stack.h b/ods/src/ods/array_stack.h
index 952a0c5..5449576 100644
--- a/ods/src/ods/array_stack.h
+++ b/ods/src/ods/array_stack.h
@@ -11,9 +11,13 @@ template<typename T>
 class ArrayStack {
 public:
 	ArrayStack(int len) : n(0), a(Array<T>(len)) {}
-	int size(void) { return a.length; }
+	int size(void) { return n; }
+	int cap(void)  { return a.length; }
 	T get(int i) { return a[i]; }
-	T set(int i, T x) { 
+	T set(int i, T x) {
+		if (i > n) {
+			n = i+1;
+		}
 		T y = a[i];
 		a[i] = x;
 		return y;
@@ -35,7 +39,6 @@ public:
 	T remove(int i) {
 		T x = a[i];
 		for (int j = i; j < (n-1); j++) {
-			std::cout << j << "\t" << i << "\t" << a[j] << std::endl;
 			a[j] = a[j+1];
 		}
 		n--;
@@ -47,7 +50,26 @@ public:
 		return x;
 	}
 
-	void resize(void) {}
+	static inline int max(int x, int y) {
+		return x > y ? x : y;
+	}
+
+	void resize(void) {
+		int nlen = max(2 * n, 1);
+		Array<T> b(nlen);
+		for (int i = 0; i < n; i++) {
+			b[i] = a[i];
+		}
+		a = b;
+	}
+
+	T pop(void) {
+		return a.remove(n - 1);
+	}
+
+	void push(T x) {
+		return a.add(n, x);
+	}
 private:
 	int		n;
 	Array<T>	a;