let x1, x2 be object ; :: thesis: {x1,x1,x1,x1,x1,x1,x2} = {x1,x2}
thus {x1,x1,x1,x1,x1,x1,x2} = {x1,x1,x2} by Th49
.= {x1,x2} by Th30 ; :: thesis: verum