Add comment re issue
@@ -1001,6 +1001,8 @@ cdef int set_children_from_heads(TokenC* tokens, int length) except -1:
tokens[i].l_edge = i
tokens[i].r_edge = i
# Three times, for non-projectivity
+ # See issue #3170. This isn't a very satisfying fix, but I think it's
+ # sufficient.
for loop_count in range(3):
# Set left edges
for i in range(length):
