theorem
  [x,y] in Proportionality_as_EqRel_of V implies x is Element of V & y
  is Element of V
proof
  assume [x,y] in Proportionality_as_EqRel_of V;
  then ex u,v st x=u & y=v & are_Prop u,v by Def3;
  then reconsider x,y as Element of V;
  x is Element of V & y is Element of V;
  hence thesis;
end;
