public static int hash <EqK, K, V>(HashMap <EqK, K, V> xs) where EqK : struct, Eq <K> => xs.GetHashCode();
public static int hash <K, V>(HashMap <K, V> xs) => xs.GetHashCode();
public static int hash <EqK, K, V>(HashMap <EqK, K, V> xs) where EqK : struct, Eq <K> => xs.GetHashCode();
public static int hash <K, V>(HashMap <K, V> xs) => xs.GetHashCode();