(a) In this section, ''qualifying child'', in relation to any claimant and year of assessment, means -
(i) a child -
(I) born in the year of assessment,
(II) who, at the commencement of the year of assessment, is under the age of 18 years, or
(III) who, if over the age of 18 years at the commencement of the year of assessment -
(A) is receiving full-time instruction at any university, college, school or other educational establishment, or
(B) is permanently incapacitated by reason of mental or physical infirmity from maintaining himself or herself and had become so permanently incapacitated before he or she had attained the age of 21 years or had become so permanently incapacitated after attaining the age of 21 years but while he or she had been in receipt of such full-time instruction,
and
(ii) a child who is a child of the claimant or, not being such a child, is in the custody of the claimant and is maintained by the claimant at the claimant's own expense for the whole or part of
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