@book{23,
	author = {Head, George O},
	title = {Autocad productivity book : the non-programmer's guide to customizing autocad--for release 13 for windows /  James L. Brittain, George O. Head & A. Ted Schaefer..- 6th ed.},
	address = {Chapel Hill, NC : Ventana Press, C1994.},
	edition = {6E}
}