reserve i,j,k,l for natural Number;
reserve A for set, a,b,x,x1,x2,x3 for object;
reserve D,D9,E for non empty set;
reserve d,d1,d2,d3 for Element of D;
reserve d9,d19,d29,d39 for Element of D9;
reserve p,q,r for FinSequence;

theorem Th57:
  for a being object holds 1 |-> a = <*a*>
proof let a be object;
  1 in Seg 1;
  then len(1 |-> a) = 1 & (1 |-> a).1 = a by CARD_1:def 7,FUNCOP_1:7;
  hence thesis by FINSEQ_1:40;
end;
