What's the difference between book and market value?

$1)$ Book value is equal to market value, while market value is equal to discount price.

$2)$ Book value is what the firm paid for an asset, while market value is the price the firm can sell an asset $3)$ BOOK value is what a firm can sell any asset for, while market value is how much competitors pay for an asset.

$4)$ Book value is always $$100,$ while market value constantly changes.