"apt-mark showmanual" will show you all packages that you have manually installed
"apt-mark showauto" will show you all packages that are automatically installed
"apt-mark showinstall" will show you all the packages that are installed
How is this useful? It tells you what packages are installed in your system.
So you can go "apt-mark showinstall | grep somelibrary" to see if you have a particular library installed that's a dependency.
Cisco 2801 Integrated Services Router ISR w/ WIC-1DSU-1-v2, VIC2-2FXS CISCO2801
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$38.99
Genuine Cisco SFP-10G-SR V03 10GBASE-SR SFP+ Transceiver Module 10-2415-03
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Cisco WS-C3850-48F-S Catalyst 3850 48x 1GB PoE+ RJ-45 1x Module Switch
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Cisco Catalyst C9200-48P-A 48 Port Rack Mountable Network Switch
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