let y3, X1, X2, X3, X4, X5, X6, X7, X8, X9 be set ; :: thesis: for x being Element of [:X1,X2,X3,X4,X5,X6,X7,X8,X9:] st X1 <> {} & X2 <> {} & X3 <> {} & X4 <> {} & X5 <> {} & X6 <> {} & X7 <> {} & X8 <> {} & X9 <> {} & ( for xx1 being Element of X1
for xx2 being Element of X2
for xx3 being Element of X3
for xx4 being Element of X4
for xx5 being Element of X5
for xx6 being Element of X6
for xx7 being Element of X7
for xx8 being Element of X8
for xx9 being Element of X9 st x = [xx1,xx2,xx3,xx4,xx5,xx6,xx7,xx8,xx9] holds
y3 = xx3 ) holds
y3 = x `3
let x be Element of [:X1,X2,X3,X4,X5,X6,X7,X8,X9:]; :: thesis: ( X1 <> {} & X2 <> {} & X3 <> {} & X4 <> {} & X5 <> {} & X6 <> {} & X7 <> {} & X8 <> {} & X9 <> {} & ( for xx1 being Element of X1
for xx2 being Element of X2
for xx3 being Element of X3
for xx4 being Element of X4
for xx5 being Element of X5
for xx6 being Element of X6
for xx7 being Element of X7
for xx8 being Element of X8
for xx9 being Element of X9 st x = [xx1,xx2,xx3,xx4,xx5,xx6,xx7,xx8,xx9] holds
y3 = xx3 ) implies y3 = x `3 )
assume that
A1: ( X1 <> {} & X2 <> {} & X3 <> {} & X4 <> {} & X5 <> {} & X6 <> {} & X7 <> {} & X8 <> {} & X9 <> {} ) and
A2: for xx1 being Element of X1
for xx2 being Element of X2
for xx3 being Element of X3
for xx4 being Element of X4
for xx5 being Element of X5
for xx6 being Element of X6
for xx7 being Element of X7
for xx8 being Element of X8
for xx9 being Element of X9 st x = [xx1,xx2,xx3,xx4,xx5,xx6,xx7,xx8,xx9] holds
y3 = xx3 ; :: thesis: y3 = x `3
x = [(x `1),(x `2),(x `3),(x `4),(x `5),(x `6),(x `7),(x `8),(x `9)] by A1, Th182;
hence y3 = x `3 by A2; :: thesis: verum