theorem for p,q being FinSequence st p is non empty holds (p^q).1=p.1
proof
let p,q be FinSequence; assume p is non empty; then reconsider
p as non empty FinSequence; set n=len p;
1<=1 & 1<=n by NAT_1:14; then 1 in Seg n; then
1 in dom p by FINSEQ_1:def 3; hence thesis by FINSEQ_1:def 7;
end;
