obtaining array key from a value

Hello

assuming I have the following array definition:

[code=php]
<?php
$a = Array(‘a’ => ‘one’, ‘b’ => ‘two’, ‘c’ => ‘three’, ‘d’ => ‘four’);
?>
[/code]

I have a variable holding one of the array’s values (for example, ‘four’). Is there a php function which can give me the key that matches that value in the array? For example, in this case the key would be ‘d’

thanks in advance

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