"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.
VINTAGE OEM IBM Three-Button ScrollPoint Optical USB Mouse (P/N:24P0494)-Grade B
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14 x 5M/16ft - LC/LC Fibre Cable 50/125 - IBM OEM - PN 12R9914 EC J14853
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Vintage Apple OEM - IBM WDS-L160 50-Pin SCSI HDD 160MB, Powers On
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Genuine IBM AC/DC Power Adapter Charger 45W for Thinkpad 310 Laptop OEM w/PC
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OEM IBM Thinkpad Keyboard 46H3846
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OEM IBM Lenovo 16V Adapter for Laptop Thinkpad 240 385 390 560 600 765 770 n/PC
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5M/16ft - LC/LC Fibre Cable 50/125 - IBM OEM - PN 12R9914 EC J14853 OFNP - New
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IBM DOS 6.1 OEM VERSION 5.25" DISKS NEW SEALED
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Lexmark/IBM 6190653 Black Developer (500k Pages), for the Lexmark 3835 printer
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IBM OEM DBOA-2720 720MB 2.5" IDE 44-Pin LAPTOP HARD DRIVE HDD Vintage TESTED
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