diff --git a/README.md b/README.md
index 4f06730..f0cde6c 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,40 @@
 # testgen
 
-A Clojure library designed to ... well, that part is up to you.
+A Clojure library designed to generate charaterisation tests.
 
 ## Usage
 
-FIXME
+At this stage, try
+
+    (testgen <function-source>)
+
+It will attempt to generate as Clojure source a set of clojure.test test definitions
+for the code passed. For example:
+
+    user=> (pprint (testgen '(defn testgen [fndef] 
+      #_=> (cond (= (first fndef) 'defn)
+      #_=> (let [name (first (rest fndef))]
+      #_=> (list 'deftest (symbol (str "test-" name))
+      #_=> (map #(write-test name %) (find-interesting-args fndef))))))
+      #_=> )
+      #_=> )
+    (deftest
+     test-testgen
+     ((is (= (testgen nil) nil))
+      (is (= (testgen ()) nil))
+      (is (thrown? java.lang.IllegalArgumentException (testgen true)))
+      (is (= (testgen "test") nil))
+      (is (thrown? java.lang.IllegalArgumentException (testgen :test)))
+      (is (thrown? java.lang.IllegalArgumentException (testgen 0)))
+      (is
+       (thrown?
+        java.lang.IllegalArgumentException
+        (testgen Integer/MAX_VALUE)))
+      (is (thrown? java.lang.IllegalArgumentException (testgen 1.0E-4)))
+      (is (thrown? java.lang.IllegalArgumentException (testgen -1.0E-4)))
+      (is (= (testgen "test-") nil))))
+
+Note, however, that it only works if the function for which tests are being generated already exists in the environment.
 
 ## License
 
diff --git a/src/testgen/core.clj b/src/testgen/core.clj
index f7f8138..aec04b6 100644
--- a/src/testgen/core.clj
+++ b/src/testgen/core.clj
@@ -5,6 +5,7 @@
      	(list 'is (list '= (list fnname arg) (eval (list fnname arg))))
 	(catch Exception e (list 'is (list 'thrown? (.getClass e) (list fnname arg))))))
 
+
 (defn constant? [arg]
 	(not (or
 		(symbol? arg)
@@ -14,11 +15,11 @@
 
 (def generic-args '(nil () true "test" :test 0 Integer/MAX_VALUE 0.0001 -0.0001))
 
-(defn find-interesting-args [sexpr]
-	"Find things in sexpr which would be interesting if passed as arguments to it"
-	(filter constant? (flatten sexpr)))
+(defn constants [form]
+	"return a list of all elements in this form which are constants"
+  (filter constant? (flatten form)))
 
-(defn find-more-interesting-args [sexpr]
+(defn find-interesting-args [sexpr]
 	"Find things in sexpr which would be even more interesting if passed as arguments to it"
 	(concat generic-args
 		(flatten 
@@ -26,11 +27,15 @@
 				#(cond 
 					(number? %) (list % (inc %) (dec %)) 
 					true %) 
-				(find-interesting-args sexpr)))))
+				(constants sexpr)))))
 
 (defn testgen [fndef] 
 	(cond (= (first fndef) 'defn)
 		(let [name (first (rest fndef))]
 			(list 'deftest (symbol (str "test-" name))
-				(map #(write-test name %) (find-more-interesting-args fndef))))))
+				(map #(write-test name %) (find-interesting-args fndef))))))
+
+;; (defn gen-tests [fnname form]
+;;   (map (partial write-test fnname) (constants form)))
+