match x.pos, y.pos with
| a,b when a == b -> true
| Or(xf1, xf2), Or(yf1, yf2)
| And(xf1, xf2), And(yf1,yf2) -> (xf1 == yf1) && (xf2 == yf2)
match x.pos, y.pos with
| a,b when a == b -> true
| Or(xf1, xf2), Or(yf1, yf2)
| And(xf1, xf2), And(yf1,yf2) -> (xf1 == yf1) && (xf2 == yf2)