/usr/lib/mono/xbuild/ is in fsharp 4.0.0.4+dfsg2-2.
This file is owned by root:root, with mode 0o755.
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/usr/lib/mono/xbuild/Microsoft/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v/FSharp/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v/FSharp/Microsoft.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v/FSharp/Microsoft.Portable.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v11.0/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v11.0/FSharp/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v11.0/FSharp/Microsoft.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v11.0/FSharp/Microsoft.Portable.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v12.0/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v12.0/FSharp/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v12.0/FSharp/Microsoft.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v12.0/FSharp/Microsoft.Portable.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v14.0/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v14.0/FSharp/
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v14.0/FSharp/Microsoft.FSharp.Targets
/usr/lib/mono/xbuild/Microsoft/VisualStudio/v14.0/FSharp/Microsoft.Portable.FSharp.Targets