public static bool exists <T>(Option <T> option, Func <T, bool> pred) => option.Exists(pred);
public static bool exists <T>(Option <T> option, Func <T, bool> Some, Func <bool> None) => option.Exists(Some, None);
public static bool exists <A>(Option <A> option, Func <A, bool> pred) => option.Exists(pred);