x <- taxonomy(c('Carnivora', 'Felidae', 'Panthera', 'Panthera leo',
'Panthera tigris', 'Ursidae', 'Ursus', 'Ursus arctos'),
supertaxa = c(NA, 1, 2, 3, 3, 1, 6, 7))
n_leaves(x)
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