The webapp provides for each item the link on ECB's website.
Speeches for : Willem F. Duisenberg where "optimal" appeared
2002-10-08 : The integration of Europe's financial markets2002-06-13 : The euro as a catalyst for integration and competition in EMU
2001-12-13 : ECB press conference on the occasion of the Signing of the Agreement between the European Central Bank and Europol