Complex sentence: In years when 8 December falls on Sunday, the Solemnity of the Immaculate Conception is normally transferred to 9 December, as it is outranked by the Second Sunday of Advent; the precept to attend mass, however, is abrogated by the transfer.
Split into simpler sentences: In years when 8 December falls on Sunday, the Solemnity of the Immaculate Conception is normally transferred to 9 December, as it is outranked by the Second Sunday of Advent. In this case, the precept to attend mass, however, is abrogated by the transfer.