Patents are exclusive, that is, others cannot exploit their patents without the permission of the patentee (designated as obligee A).
However, patents are sometimes based on other patents, so the patentee A cannot exploit his own patent without the permission of the patentee (designated as the obligee B).
So patents can prevent others from using them, but they can't guarantee that they can use them.
In addition, there is also a kind of patent license, that is, exclusive license, that is, within the time limit stipulated in the contract, except the licensee, even the patentee himself cannot implement it.
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