three­col­umn – LaTeX out­put in three columns

An ex­ten­sion to the LaTeX 2.09 out­put rou­tine that al­lows three (equal width) col­umn out­put.
Three-col­umn out­put does not per­mit multi-col­umn floats, and there are prob­lems switch­ing from three- to one- or two-col­umn set­ting. (Users should be aware that the pack­age may not work with a cur­rent LaTeX ker­nel.)