let x1, x2, x3, x4, x5, x6 be set ; :: thesis: {x1,x1,x1,x2,x3,x4,x5,x6} = {x1,x2,x3,x4,x5,x6}
thus {x1,x1,x1,x2,x3,x4,x5,x6} = {x1,x1,x2,x3,x4,x5,x6} by Th75
.= {x1,x2,x3,x4,x5,x6} by Th74 ; :: thesis: verum