take y3 ; :: thesis: for y1, y2, y3, y4, y5 being object st x = [y1,y2,y3,y4,y5] holds
y3 = y3
thus for y1, y2, y3, y4, y5 being object st x = [y1,y2,y3,y4,y5] holds
y3 = y3 by A1, Th10; :: thesis: verum