John gives a gift of shares and cash to Séamus.
The total CAT on the gift is €900 (€500 of this applies to the shares).
Only the shares are liable for CGT. The CGT payable on the shares is €600.
The credit for CGT on the shares cannot be greater than the amount of CAT on the shares.
Therefore the credit for CGT paid is €500 (not €600) and this is what Séamus may claim.
The revised CAT to be paid by Séamus is €400 (€900-€500).