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~ # apt -t stretch-backports install libreoffice                                                                             [R130 J0 L:1.15 1.09 0.67 U:1+13:04 pts/2 2345H]

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libreoffice : Depends: libreoffice-core (= 1:6.1.5-3+deb10u4~bpo9+1) but 1:5.2.7-1+deb9u11 is to be installed
               Recommends: fonts-noto-core but it is not installable
               Recommends: fonts-noto-ui-core but it is not installable
               Recommends: libreoffice-java-common (>= 1:6.1.5~) but 1:5.2.7-1+deb9u11 is to be installed
E: Unable to correct problems, you have held broken packages.