Not a DOI

The resolution service at https://doi.org resolves DOIs. You have attempted to resolve pl/wydawnictwa/probability_and_mathematical_statistics, which is not a DOI.

pl/wydawnictwa/probability_and_mathematical_statistics may be a Handle (DOIs are a special sort of Handle). If pl/wydawnictwa/probability_and_mathematical_statistics is a valid Handle you should be able to resolve it at https://hdl.handle.net.