/usr/lib/mono/xbuild/ is in mono-xbuild 3.2.8+dfsg-4ubuntu1.
This file is owned by root:root, with mode 0o755.
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/usr/lib/mono/xbuild-frameworks/.NETFramework/
/usr/lib/mono/xbuild-frameworks/.NETFramework/v2.0/
/usr/lib/mono/xbuild-frameworks/.NETFramework/v2.0/RedistList/
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/usr/lib/mono/xbuild-frameworks/.NETFramework/v4.0/RedistList/
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