Danbury-based Praxair and Linde AG have entered into a definitive business combination agreement to merge.  The companies would form a new holding company through an all-stock transaction, consistent with the one they announced in December.  The agreement is subject to regulatory approval. In a news release, Praxair said the merger will create the world’s largest industrial gas company with a combined market value of more than $70 billion.  The merger will retain the Munich company's name, though they would be equal partners.  Praxair recently moved it's headquarters to Berkshire Corporate Park and officials expect to keep a significant presence in Danbury.