Booleans don't appear on the tag browser.
There's a workaround that you can use a composite column (column built from other column) and tick the 'show in tag browser' button. Something like this should work.
Code:
program:
if
check_yes_no('#mybool', 1, 0, 0)
then
'Undefined'
elif
check_yes_no('#mybool', 0, 1, 0)
then
'No'
elif
check_yes_no('#mybool', 0, 0, 1)
then
'Yes'
fi