Must a woman whose marriage contract is invalid be divorced or have the contract annulled before marrying another man?

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If a woman enters into an invalid marriage contract (*tazwij fāsid*), she cannot marry another man until the first husband divorces her or the judge annuls the marriage (*faskh*). If the husband refuses to divorce, the judge must annul the marriage. This position is adopted by Ahmad. The evidence for requiring an act of separation is that this marriage is one where ijtihad (independent legal reasoning) is permissible in its validity, thus requiring a formal separation, similar to a sound but disputed marriage. Furthermore, marrying her to another without separation leads to two husbands each believing their own contract to be valid while considering the other's invalid, which must be prevented.