public static (SG s1, SG s2, SG s3, SG s4, DN n1, DN n2) Flip(DN curr, DN pair, SG prv, V2 p_curr, V2 p_pair)
{
var alt = new SG(p_curr, p_pair);
var na = new DN(alt, prv.a);
var nb = new DN(alt, prv.b);
na.neighbor.Add(nb);
nb.neighbor.Add(na);
var s1 = new SG(prv.a, p_curr);
var s2 = new SG(prv.a, p_pair);
var s3 = new SG(prv.b, p_curr);
var s4 = new SG(prv.b, p_pair);
na.SetNeighborWhenFlip(s1, curr);
na.SetNeighborWhenFlip(s2, pair);
nb.SetNeighborWhenFlip(s3, curr);
nb.SetNeighborWhenFlip(s4, pair);
return(s1, s2, s3, s4, na, nb);
}