ged ▁documents ▁that ▁def ended ▁the ▁authentic ity ▁of ▁the ▁Lib ell us ▁and ▁attempted ▁to ▁explain ▁why ▁it ▁permitted , ▁or ▁( to ▁those ▁who ▁followed ▁the ▁" R oman " ▁system ) ▁seemed ▁to ▁permit , ▁nie ces ▁to ▁marry ▁their ▁un cles , ▁or ▁even ▁first ▁c ous ins ▁to ▁marry . ▁ ▁Bon if ace ' s ▁doub ts ▁about ▁the ▁Lib ell us ▁were ▁rev ived ▁in ▁the ▁tw enti eth ▁century ▁by ▁several ▁modern ▁histor ians . ▁In ▁ 1 9 4 1 ▁Sus o ▁Bre chter ▁made ▁a ▁study ▁of ▁the ▁historical ▁sources ▁for ▁Gregory ▁the ▁Great ' s ▁Ang lo - S ax on ▁mission . ▁In ▁this ▁study ▁Bre chter ▁attempted ▁to ▁prove ▁that ▁the ▁Lib ell us ▁was ▁an ▁e ighth - century ▁forg ery ▁by ▁N oth helm . ▁He ▁believed ▁that ▁the ▁Lib ell us ▁contained ▁too ▁much ▁that ▁per tain ed ▁specifically ▁to ▁e ighth - century ▁( r ather ▁than ▁late ▁sixth - century ) ▁the ological ▁concerns , ▁i . e . ▁the ▁concerns ▁of ▁N oth helm ▁rather ▁than ▁August ine . ▁He ▁argued ▁that ▁the ▁forg ery ▁was ▁completed ▁in ▁ 7 3 1 ▁and ▁was ▁fo isted ▁on ▁B ede ▁by ▁N oth helm ▁in ▁that ▁year , ▁making ▁it ▁a ▁late ▁insert ion ▁into ▁B ede ' s ▁Historia . ▁Bre chter ' s ▁work ▁did ▁not ▁attract ▁much ▁scholar ly ▁interest ▁until ▁ 1 9 5 9 , ▁when ▁Margaret ▁De anes ly