for G being Graph
for vs, vs1, vs2 being FinSequence of the carrier of G
for c, c1, c2 being Chain of G st vs1 is_vertex_seq_of c1 & vs2 is_vertex_seq_of c2 & vs1 . (len vs1) = vs2 . 1 & c = c1 ^ c2 & vs = vs1 ^' vs2 holds
vs is_vertex_seq_of c