Since trees are combined only when the degrees of their roots are equal, it must have been that yi also had degree at least i-1 at the time it became a child of x.
چون درخت‌های فقط زمانی با هم ادغام می‌شوند که درجه ریشه هایشان برابر باشد، نتیجه می‌شود که yi زمانی که فرزند x می‌شد حداقل از درجه i-۱ بوده.