reserve x,y,z for set;
reserve f,f1,f2,f3 for FinSequence,
  p,p1,p2,p3 for set,
  i,k for Nat;
reserve D for non empty set,
  p,p1,p2,p3 for Element of D,
  f,f1,f2 for FinSequence of D;

theorem Th79:
  p..(f:-p) = 1
proof
  (f:-p)/.1 = p by FINSEQ_5:53;
  hence thesis by Th43;
end;
