The `IEEETran.bst` uses `\providecommand`, which is core LaTeX (more text: https://tex.stackexchange.com/q/36175/9075). `\providecommand` should be handled as `\newcommand` in the context of SnuggleTeX.
The
IEEETran.bstuses\providecommand, which is core LaTeX (more text: https://tex.stackexchange.com/q/36175/9075).\providecommandshould be handled as\newcommandin the context of SnuggleTeX.