theorem Th27:
  not nt is one-to-one implies Det Segm(M,nt,nt1) = 0.K
proof
  assume not nt is one-to-one;
  then consider x,y being object such that
A1: x in dom nt and
A2: y in dom nt and
A3: nt.x=nt.y and
A4: x<>y;
A5: dom nt=Seg n by FINSEQ_2:124;
  then consider i be Nat such that
A6: x=i and
A7: 1<=i and
A8: i<=n by A1;
  consider j be Nat such that
A9: y=j and
A10: 1<=j and
A11: j<=n by A2,A5;
A12: j in Seg n by A10,A11;
  i in Seg n by A7,A8;
  hence thesis by A3,A4,A6,A9,A12,Th26;
end;
