\directlua{
local ffi = require("ffi")
ffi.cdef[[
/* from tex/equivalents.h */
typedef enum {
bottom_level = 0,
simple_group,
hbox_group,
adjusted_hbox_group,
vbox_group,
vtop_group,
align_group,
no_align_group,
output_group,
math_group,
disc_group,
insert_group,
vcenter_group,
math_choice_group,
semi_simple_group,
math_shift_group,
math_left_group,
local_box_group,
split_off_group,
split_keep_group,
preamble_group,