Is it permissible for a man to marry a fourth woman while his wife, divorced with a first repudiation, is still observing her waiting period (iddah)?

It is not permissible to marry a fourth wife before the completion of the 'iddah (waiting period) of a woman divorced with a revocable divorce, by the consensus of Muslims, because she is considered to be like a wife. As for an irrevocable divorce, marrying a fifth wife is permissible, though there is a difference of opinion among scholars, and it is more prudent to avoid it until the 'iddah of the divorced woman is completed.