CHICAGO (AP) _ Grain futures were mixed in early trading Monday on the Chicago Board of Trade. Dec. corn was down 1.5 cents at $4.54 a bushel. Dec. wheat was unchanged at $6.25 a bushel. Dec. oats was unchanged at $3.72 a bushel. Nov. soybeans was down 6.5 cents at $12.50 a bushel. Beef was...