Multi-speed Europe or two-speed Europe (called also "variable geometry Europe" or "Core Europe" depending on the form it would take in practice) is the idea that different parts of the European Union should integrate at different levels and pace depending on the political situation in each individual country. Indeed, multi-speed Europe is currently a reality, with only a subset of EU countries being members of the eurozone and of the Schengen area. Like other forms of differentiated integration such as à la carte and variable geometry, "multi-speed Europe" arguably aims to salvage the "widening and deepening of the European Union" in the face of political opposition. Reasons and actuality of the concept The concept entered political discourse when, after the end of the Cold War, an eastward enlargement of the European Union began to materialise and the question arose how "widening" could be made compatible with "deepening", i.e., how the imminent enlargement process could be prevented from diluting the idea of an "ever closer union among the peoples of Europe", as the Treaty establishing the European Economic Community of 1957 had put it. In 1994 – still at a time of the EU12 – the German Christian Democrats Wolfgang Schäuble and Karl Lamers published a document in which they called for a Kerneuropa (= core Europe). This idea envisaged that "core Europe" would have a "centripetal effect", a magnetic attraction for the rest of Europe. A precursor to that concept had been a proposal by two advisors to German Chancellor Helmut Kohl, Michael Mertes and Norbert J. Prill, published as early as July 1989. Mertes and Prill called for a concentric circles Europe, built around a federal core consisting of the Inner Six (EU6) and like-minded EU member states. In 1994 they partly revoked their original idea, arguing that the post-Cold War EU would rather look like a "Europe of Olympic rings" than a "Europe of concentric circles". The multi-speed Europe concept has been debated for years in European political circles, as a way to solve some institutional issues. The concept is that the more members there are in the Union, the more difficult it becomes to reach consensus on various topics, and the less likely it is that all would advance at the same pace in various fields. Intermediate forms could be limited to some areas of close cooperation, as some historical examples are given below. It is also