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Mass Twice in One Day?
With Christmas on Monday, we have the obligation to go on Sunday the 24th for the 4th week in Advent and, again, for Christmas, whether later in the day for one of the vigil Masses for Christmas or on Christmas day. Sorry, no two for one deals such as going to the Vigil Mass on Christmas eve and counting it also for Sunday. Here is an article on this with a options for fulfilling both obligations:
http://www.catholicherald.co.uk/commentandblogs/2017/12/05/do-i-have-to-go-to-mass-twice-on-christmas-eve-this-year/