The leaders of the euro zone’s four largest economies vowed on Friday to defend the common currency with all means necessary, trying to reassure markets before yet another key summit meeting of the European Union next week in Brussels. But there clear disagreement remains about what those mechanisms ought to be. Chancellor Angela Merkel of Germany, who has been under increasing pressure from the other three leaders — and from the International Monetary Fund — to do more to support the euro zone and its banks, gave little indication on Friday that she was warming up to calls for collectivized debt or for the use of ... (full story)