Bruce I. Mills Martha W. Evens Reva Freedman Implementing Directed Lines of Reasoning in an Intelligent Tutoring System Using the Atlas Planning Environment. 729- 2004 conf/itcc/2004-1 ITCC (1) http://csdl.computer.org/comp/proceedings/itcc/2004/2108/01/210810729abs.htm db/conf/itcc/itcc2004-1.html#MillsEF04