let D be non empty set ; :: thesis: for z being Tuple of 3,D ex d1, d2, d3 being Element of D st z = <*d1,d2,d3*>
let z be Tuple of 3,D; :: thesis: ex d1, d2, d3 being Element of D st z = <*d1,d2,d3*>
A: z is Element of D * by FINSEQ_1:def 11;
len z = 3 by FINSEQ_1:def 18;
then z in 3 -tuples_on D by A;
then z in { <*d1,d2,d3*> where d1, d2, d3 is Element of D : verum } by Th122;
hence ex d1, d2, d3 being Element of D st z = <*d1,d2,d3*> ; :: thesis: verum