You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Treaty

Context:
A treaty is null and void if it is in violation of a peremptory norm. These norms, unlike other principles of customary law, are recognized as permitting no violations and so cannot be altered through treaty obligations. These are limited to such universally accepted prohibitions as those against the aggressive use of force, genocide and other crimes against humanity, piracy, hostilities directed at civilian population, racial discrimination and apartheid, slavery and torture, meaning that no state can legally assume an obligation to commit or permit such acts.

Question:
What type of norm is recognized as permitting no violations and so cannot be altered through treaty obligations?

peremptory norm