Marked_+Marked_minus+minuxMarked_minuxminuszyxminus(minus(x))xminux(+(x,y))+(minus(y),minus(x))+(minus(x),+(x,y))y+(+(x,y),minus(y))xminus(minus(x))xminux(+(x,y))+(minus(y),minus(x))+(minus(x),+(x,y))y+(+(x,y),minus(y))xMarked_minux(+(x,y))Marked_+(minus(y),minus(x))Marked_minux(+(x,y))Marked_minus(y)Marked_minux(+(x,y))Marked_minus(x)