let X1, X2, X3, X4, X5, X6, X7, X8 be set ; :: thesis: [:X1,X2,X3,X4,X5,X6,X7,X8:] = [:[:X1,X2,X3:],X4,X5,X6,X7,X8:]
thus [:X1,X2,X3,X4,X5,X6,X7,X8:] = [:[:[:[:[:[:[:X1,X2:],X3:],X4:],X5:],X6:],X7:],X8:] by Th126
.= [:[:[:X1,X2:],X3:],X4,X5,X6,X7,X8:] by Th47
.= [:[:X1,X2,X3:],X4,X5,X6,X7,X8:] by ZFMISC_1:def 3 ; :: thesis: verum