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The version of Mamba running on GRACE expects the bash variable $MAMBA_ROOT_PREFIX to be set to the same place as your default conda directory. By default this location is ~/.conda but you might need to set it to something else if you decide to use your own personal copy of conda instead of the admin maintained conda instance.
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Micromamba is a pure C++ executable binary and is maintained by the same team as Mamba. Since Micromamba does not depend on python to function, it can be used seamlessly as a drop in replacement for conda. In addition, due to the use of a single binary upgrading Mamba will be seamless as new versions are released.