The fetus, the yavam, betrothal, the deaf-mute, and a boy nine years and one day [old] disqualify but do not entitle [a woman] to eat [terumah]; [and even if] it is in doubt whether the boy was nine years and one day [old] or not, [or] whether two hairs had appeared or not.  [If] a house collapsed on a man and his brother's daughter and it is not known who died first, her co-wife requires chalitzah but may not be taken in yibum.