
theorem Th4:
  for n being Nat st 1 < n holds 0.(Z/n) = 0
   proof
     let n be Nat;
     Z/n = doubleLoopStr(#Segm(n),addint(n),multint(n),In(1,Segm(n)),
                          In(0,Segm(n))#) by INT_3:def 12;
     hence thesis by NAT_1:44,SUBSET_1:def 8;
   end;
