reserve p, q for FinSequence,
  e,X for set,
  i, j, k, m, n for Nat,
  G for Graph;
reserve x,y,v,v1,v2,v3,v4 for Element of G;

theorem Th1:
  e orientedly_joins v1, v2 implies e joins v1, v2
by GRAPH_1:def 12;
