I start lyx, create a new document, insert math->cases environment, view dvi. I get two ERRORS!
This is because the default document style article does not have amsmath. The solution is either adding \usepackage{amsmath} in the preamble or using another document style like article(AMS). This is not a big prolem but it would be better to avoid this kind of problem by adding amsmath to the default style. Thanks. -- Bo Peng