reserve a,a1,a2,b,c,d for Ordinal,
  n,m,k for Nat,
  x,y,z,t,X,Y,Z for set;
reserve f,g for Function;
reserve A,B,C for array;
reserve O for connected non empty Poset;
reserve R,Q for array of O;
reserve T for non empty array of O;
reserve p,q,r,s for Element of dom T;

theorem Th80:
  last <%x%> = x
  proof
    dom <%x%> = succ 0 by AFINSQ_1:def 4; then
    union dom <%x%> = 0 by ORDINAL2:2;
    hence thesis;
  end;
