"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.
SFP-10G-LR Compatible 10GBase-LR SFP+ LR Transceiver 10G 1310nm SMF up ot 10km
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Cisco SG110 24 Port Gigabit Ethernet Switch w/ 2 x SFP SG110-24
$117.00
Allen-Bradley 1783-SFP1GSX Compatible 1000BASE-SX SFP 850nm 550m Transceiver-895
$65.50
Genuine Cisco SFP-10G-SR V03 10GBASE-SR SFP+ Transceiver Module 10-2415-03
$8.00
NEW Sealed Cisco SFP-10G-LR 10GBASE-LR SFP+ 1310nm 10km *US Shipping*
$18.00
Cisco QSFP-40G-SR-BD BiDi Short-reach Transceiver, 1 Year Warranty
$17.25
Cisco SFP-10G-LR-S SFP+ 1310nm 10km DOM Transceiver Module 10-3107-01 - 1 Year
$41.59
Cisco Meraki MA-SFP-10GB-SR 10G SFP+ SR 850nm 300m LC MMF
$29.99
LOT OF 20 Genuine Cisco SFP-10G-SR V03 10GBASE-SR SFP+ Transceiver Module
$89.00