Sentence:  The proof of toroidalization of <WSD>morphisms</WSD> of 3-folds to surfaces in [C3] breaks up into two parts: a reduction to prepared <WSD>morphisms</WSD> and then a proof of toroidalization of prepared <WSD>morphisms</WSD> from "n"-folds to [surfaces] in [CK]. 
Meaning of the word marked with <WSD> tags:  ("formally") An arrow in a category; ("less formally") an abstraction that generalises a map from one mathematical object to another and is structure-preserving in a way that depends on the branch of mathematics from which it arises.