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diff --git a/gr-howto-write-a-block/include/howto/square2_ff.h b/gr-howto-write-a-block/include/howto/square2_ff.h
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+/* -*- c++ -*- */
+/*
+ * Copyright 2004,2012 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ *
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDED_HOWTO_SQUARE2_FF_H
+#define INCLUDED_HOWTO_SQUARE2_FF_H
+
+#include <howto/api.h>
+#include <gr_sync_block.h>
+
+namespace gr {
+  namespace howto {
+
+    /*!
+     * \brief square2 a stream of floats.
+     * \ingroup block
+     *
+     * This uses the preferred technique: subclassing gr_sync_block.
+     */
+    class HOWTO_API square2_ff : virtual public gr_sync_block
+    {
+    public:
+      /*
+       * We use boost::shared_ptr's instead of raw pointers for all
+       * access to gr_blocks (and many other data structures). The
+       * shared_ptr gets us transparent reference counting, which
+       * greatly simplifies storage management issues. This is
+       * especially helpful in our hybrid C++ / Python system.
+       *
+       * See http://www.boost.org/libs/smart_ptr/smart_ptr.htm
+       *
+       * gr::howto::square2_ff::sptr
+       */
+       typedef boost::shared_ptr<square2_ff> sptr;
+
+       /*!
+	* \brief Return a shared_ptr to a new instance of howto::square2_ff.
+	*
+	* To avoid accidental use of raw pointers, howto::square2_ff's
+	* constructor is in a private implementation
+	* class. howto::square2_ff::make is the public interface for
+	* creating new instances.
+	*/
+       static sptr make();
+    };
+
+  } // namespace howto
+} // namespace gr
+
+#endif /* INCLUDED_HOWTO_SQUARE2_FF_H */