theorem
  vs is_oriented_vertex_seq_of c implies G-TVSet rng c c= rng vs
proof
  assume
A1: vs is_oriented_vertex_seq_of c;
  then
A2: len vs = len c + 1;
  let y be object;
  assume y in G-TVSet rng c;
  then consider v being Element of G such that
A3: v=y and
A4: ex e being Element of the carrier' of G st e in rng c & v = (the
  Target of G).e;
  consider e being Element of the carrier' of G such that
A5: e in rng c and
A6: v = (the Target of G).e by A4;
  consider x being object such that
A7: x in dom c and
A8: e = c.x by A5,FUNCT_1:def 3;
  reconsider x as Element of NAT by A7;
A9: 1<=x by A7,FINSEQ_3:25;
A10: x<=len c by A7,FINSEQ_3:25;
A11: 1<=x+1 by NAT_1:12;
A12: x+1<=len vs by A2,A10,XREAL_1:7;
  set v1 = vs/.x;
  set v2 = vs/.(x+1);
A13: v2 = vs.(x+1) by A2,A10,A11,FINSEQ_4:15,XREAL_1:7;
  c.x orientedly_joins v1, v2 by A1,A9,A10;
  then
A14: v = v2 by A6,A8;
  x+1 in dom vs by A11,A12,FINSEQ_3:25;
  hence thesis by A3,A13,A14,FUNCT_1:def 3;
end;
