reserve x for set,
  D for non empty set,
  k,n,m,i,j,l for Nat,
  K for Field;
reserve n,i,j for Nat;

theorem Th75:
  1<=i & i<=n implies (Base_FinSeq(n,i)).i=1
proof
A1: len (n |-> 0)=n by CARD_1:def 7;
  assume 1<=i & i<=n;
  then i in dom(n |-> 0) by A1,FINSEQ_3:25;
  hence thesis by FUNCT_7:31;
end;
