Title:    Comparing homotopy categories
Author:   David Blanc

e-mail:   blanc@math.haifa.ac.il
Address:  Department of Mathematics
          University of Haifa
          31905 Haifa
          Israel

AMS Classification:  Primary: 55U35; Secondary: 55P65, 55Q35, 18G55


          Abstract:

Given a suitable functor  T:C -> D  between model categories, we
define a long exact sequence relating the homotopy groups of any 
X in C  with those of  TX,  and use this to describe an
obstruction theory for lifting an object  G in D to C.  
Examples include finding spaces with given homology or homotopy groups.