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We present $\mathtt{bimEX}$, a Mathematica package for exact computations in3$+$1 bimetric relativity. It is based on the $\mathtt{xAct}$ bundle, which canhandle computations involving both abstract tensors and their components. Inthis communication, we refer to the latter case as concrete computations. Thepackage consists of two main parts. The first part involves the abstracttensors, and focuses on how to deal with multiple metrics in $\mathtt{xAct}$.The second part takes an ansatz for the primary variables in a chart as theinput, and returns the covariant BSSN bimetric equations in components in thatchart. Several functions are implemented to make this process as fast anduser-friendly as possible. The package has been used and tested extensively inspherical symmetry and was the workhorse in obtaining the bimetric covariantBSSN equations and reproducing the bimetric 3$+$1 equations in the sphericalpolar chart.

$\mathtt{bimEX}$: A Mathematica package for exact computations in $3+1$ bimetric relativity