Rabbi Ishmael taught that one must have three myrtle-branches, two willow-branches, one palm-branch, and one etrog. Even if two of the myrtle-branches have their tips broken off and only one is whole, the lulav set is valid. Rabbi Tarfon taught that even if all three have their tips broken off, the set is valid. Rabbi Akiva taught that just as it is necessary to have only one palm-branch and one etrog, so it is necessary to have only one myrtle-branch and one willow-branch.