Les formes irrégulières basques gauntza, zauntza, dauntza

This article tries to explain why the verb "etzan" has "natza", "hatza", "datza" as its present tense forms in the singular, whereas the plural is "gauntza", "zauntza" and "dauntza". The author also explains the different theories on the appearance of the "n" and the "u" in the plural