static L<Method> findFunctionalInterfaceMethods(Class intrface) {
  if (!isInterface(intrface)) null;
  new L<Method> l;
  _MethodCache cache = getMethodCache(intrface);
  
  Class c = intrface;
  do {
    for (Method m : c.getDeclaredMethods()) {
      S name = m.getName();
      var args = m.getParameterTypes();
      if (m.getDeclaringClass() != O.class
        && !m.isDefault() && !isStaticMethod(m) && !m.isSynthetic()
        && !(eq(name, "equals") && l(args) == 1 && args[0] == O.class))
        l.add(m);
    }

    c = c.getSuperclass();
  } while (c != null);
  
  ret l;
}