I have tried to install Sage in an old laptop with Lubuntu with the following three commands:
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$ sudo -E apt-add-repository -y ppa:aims/sagemath
$ sudo -E apt-get update
$ sudo -E apt-get install sagemath-upstream-binary
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but the last command returned
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Package sagemath-upstream-binary is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'sagemath-upstream-binary' has no installation candidate
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After downloading Sage and decompressing it, I was able to run it but, I searched a lot and, until now, could not figure out what is wrong. How can I fix this? any suggestions?