omial-time al- gorithm uses at most polynomial space. I it follows that #1' is contained in PSPACE. The notion of PSPACF.- 2 I woo reascosicsilscom 1073/ress 0709640104 hardness and PSPACE-completeness is similar to the notion of NP-hardness and NP-completenets, but with respect to the problems in PSPAC