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The theorem of Huet and Lévy stating that for orthogonal rewrite systems (i) every reducible term contains a needed redex and (ii) repeated contraction of needed redexes results in a normal form if the term under consideration has a normal form, forms the basis of all results on optimal normalizing strategies for orthogonal rewrite systems. However, needed redexes are not computable in general. In the paper we illustrate, based on the framework introduced in , how the use of approximationsdoi:10.1016/s1571-0661(04)80598-x fatcat:ircl2munrvd3heig4kdcls4kdq