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 Th59:
  for a being object holds 2 |-> a = <*a,a*>
proof let a be object;
  thus 2 |-> a = (1+1) |-> a .= (1|->a)^<*a*> by Th58
    .= <*a,a*> by Th57;
end;
