in this chapter we develop obstruction theory for the general lifting problem. A sequence of obstructions is defined whose vanishing is necessary and sufficient for the existence of a lifting. The kth obstruction in the sequence is defined if and only if all the lower obstructions are defined and vanish, in which case the vanishing of the kth obstruction is a necessary condition for definition of the (k + l)st obstruction.
KeywordsObstruction Theory Free Homotopy Class Lift Problem Weak Homotopy Cohomology Operation
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