Psd is available from the author using email, or from cs.tut.fi as the file /pub/src/languages/schemes/psd-1.1.tar.Z using anonymous ftp. Psd is placed under the GNU General Public License,so it can be freely used and distributed. The General Public License is included in the Psd distribution, or it can be obtained from the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.