i am a new PHP, i have some files like this:

In root.php i have

```
<?php
class Root
{
// Some functions here
}

```

In child\_1.php i have: 

```
class Child_1 extends Root
{
  function abc()
  {
  //Some code here
  }
}

```

In child\_2.php i have: 

```
class Child_2 extends Root
{
  function cde()
  {
  // How can i call function abc() from class Child_1 here
  }
}

```

Yes, how can i call a function of Child\_1 class from a function of Child\_2 class.