Table 1. Notations used in our model.

Symbol	Description
D	the number of documents in the corpus
V	the number of unique terms in the corpus
H	the height of the topical hierarchy
T	the total number of topics in the hierarchy
τ	the number of leaf topics in the hierarchy
Ct	the number of child topics of topic t
ld	the length (number of tokens) of document d
πt	the parent topic of topic t
χt ∈ [Cπt]	the index of topic t among its siblings
wd,j ∈ [V]	the j-th token in the document d
$z_{d,j}^i$	the child index of the topic at level i for wd,j
ϕt	topic t's multinomial distribution over terms
αt	the Dirichlet hyperparameter of topic t
θd,t	document d's distribution over t's child topics