The 4th game of the match, was a pretty sharp draw, with Muzychuk sacrificing material for a perpetual. When I see short repetitions like this I wonder if (a) they have been played before or (b) part of home preparation for one side. In this case I suspect it is the later, although it was White who chose to vary from previous games (including Fischer - Olaffson 1966), with 13.Nd4.
Hou,Yifan - Muzychuk,Mariya [C83]
2016 WOmens World Championship, 06.03.2016