
theorem Th2:
for m be non zero Nat, k be Nat, X be non-empty m-element FinSequence
 st k <= m holds
 X|k is non-empty k-element FinSequence
proof
    let m be non zero Nat, k be Nat, X be non-empty m-element FinSequence;
    assume
A1:  k <= m;
    len X = m by CARD_1:def 7; then
    len(X|k) = k by FINSEQ_1:59,A1;
    hence thesis by CARD_1:def 7;
end;
