--- a/lib/derivative_st.txt	Mon Apr 04 15:22:42 2011 +0100
+++ b/lib/derivative_st.txt	Mon Apr 04 15:26:13 2011 +0100
@@ -1,3 +1,15 @@
+
+(* Following taken directly from the IEC 61131.3 draft standard *)
+
+(*
+ * An IEC 61131-3 IL and ST compiler.
+ *
+ * Based on the
+ * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
+ *
+ *)
+
+
  FUNCTION_BLOCK DERIVATIVE
    VAR_INPUT
      RUN : BOOL ;          (* 0 = reset                  *)