The only extra work is in the Mstep, which optimizes a single (concave) objective function.
let z n denote the missing data, where, in the parallel data setting, only the alignment is missing (z n k = a n k ) and in the non-parallel data setting, both alignment and source symbol are missing (z n 1 = (a n 1 , e n ), z n 2 = (a n 2 , f n )).