An example is a contemporary responsum by Rabbi Ovadia Yosef, establishing the impossibility to prove "mamzer" status in a case where the evidence might appear to be clear-cut. The case involved the daughter of an "aguna" who had been married by a Haredi rabbi to a husband who subsequently converted to Christianity and refused to participate in a Jewish divorce. The mother eventually divorced and remarried civilly and had the daughter years later. The daughter, who had been raised as an Orthodox Jew and attended a Haredi day school, brought up the question of her status herself prior to an impending marriage. Rabbi Yosef proceeded systematically to disqualify evidence that a prior marriage had ever taken place. The mother's evidence was immediately disqualified as an interested party. The ketubah (Jewish marriage contract/certificate) was never found. The rabbi who performed the marriage was contacted, but Rabbi Yosef wrote that his testimony could not be accepted without the ketubah, and in any event required corroboration by a second witness. Attempts to contact the husband were abandoned after an adversarial conversation with his new, non-Jewish wife. Thus, Rabbi Yosef concluded there was insufficient evidence that a valid prior marriage had ever taken place. Rabbi Yosef then proceeded to establish the possibility that the former husband might be the daughter's father. The mother testified that her former husband occasionally brought alimony payments and came for visitation in person and hence the two were sometimes at least momentarily alone together. Applying an ancient rule that when a husband and wife are known to be alone together behind a closed door the law presumes sexual intercourse may well have taken place, Rabbi Yosef concluded that it was possible the former husband was the daughter's father and hence Jewish law, which very strongly construes all evidence in favour of birth within marriage, had to presume that he was. Thus, Rabbi Yosef concluded that there was insufficient evidence of either a former marriage or that the new husband was the father, and hence he concluded that no evidence of "mamzerut" had occurred.