One of the four would come under pressure and would have be surrendered in order to avoid inconsistency. The single currency was the way to square the circle in merging all the independent national monetary policies. One single money for one single market.
Tommaso saw the creation of the single currency as an ultimate integrative step, in the clearly defined policy field of monetary policy and was very aware of the responsibility given to the ECB to make this a success and a stepping stone for completing and achieving economic integration. The euro contained a strong commitment to move towards more economic integration.