Complex sentence: The 1983 constitution mandates at least three senators (or four if an attorney-general is in post), although the number can be increased by the parliament as long as it doesn't exceed two thirds of the number of representatives.
Split into simpler sentences: The 1983 constitution mandates at least three senators, or four if an attorney-general is not one of these three appointed senators. The number can be increased by the parliament as long as it doesn't exceed two thirds of the number of representatives.