The principals in the auto emissions trial to begin Tuesday in U.S. District Court in Burlington, Vt.:

n PLAINTIFFS: General Motors, Daimler Chrysler, two auto industry associations and three Vermont car and truck dealers.

n DEFENDANTS: The state of Vermont, its Agency of Natural Resources and agency Secretary George Crombie.

n INTERVENORS: State of New York, Natural Resources Defense Council, Conservation Law Foundation, Sierra Club, Environmental Defense, Vermont Public Interest Research Group.

n AT ISSUE: Vermont’s decision to adopt rules first adopted by California and then other states to lower vehicle emissions of the greenhouse gas carbon dioxide.