reserve N for PT_net_Str, PTN for Petri_net, i for Nat;

theorem Lm1:
  for D be non empty set, f be non empty FinSequence of D
  st f is circular holds f.1 = f.len f
  proof
    let D be non empty set, f be non empty FinSequence of D;
    assume
A4: f is circular;
A2: 0+1 <= len f by NAT_1:13;then
A1: 1 in dom f by FINSEQ_3:25;
A3: len f in dom f by FINSEQ_3:25,A2;
    thus f.1 = f/.1 by PARTFUN1:def 6,A1
    .= f.len f by PARTFUN1:def 6,A3,A4;
  end;
