public CorrespondenceLink()
{
LHS = new CorrespondenceNode ();
RHS = new CorrespondenceNode ();
ID = -1;
}
public CorrespondenceLink(string rhs, string lhs, int id)
{
LHS = new CorrespondenceNode(lhs, id);
RHS = new CorrespondenceNode (rhs, id);
ID = id;
}