reserve a,b,c for set;

theorem
  for D being non empty set,f being FinSequence of D st f=<*a,b*> holds
  a in D & b in D
proof
  let D be non empty set,f be FinSequence of D;
A1: f is Function of dom f,D by FINSEQ_2:26;
  assume
A2: f=<*a,b*>;
  then
A3: 1 in dom f & 2 in dom f by CALCUL_1:14;
  f.1=a & f.2=b by A2;
  hence thesis by A3,A1,FUNCT_2:5;
end;
