I want to retrieve all case-insensitive duplicate entries from an array. Is this possible in PHP?

array(
    1 => '1233',
    2 => '12334',
    3 => 'Hello',
    4 => 'hello',
    5 => 'U'
);

Desired output array:

array(
    1 => 'Hello',
    2 => 'hello'
);
php arrays duplicates filtering case-insensitive
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