reserve X,Y,x,y for set;
reserve A for non empty Poset;
reserve a,a1,a2,a3,b,c for Element of A;
reserve S,T for Subset of A;

theorem Th13:
  for A being RelStr, T being Subset of A holds the InternalRel of
  A well_orders T implies T is Chain of A
by ORDERS_1:7,Def7;
