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tax_1 

$tax_query = array(
	'relation' => 'OR',
	array(
		'relation' => 'OR',
		array(
			'taxonomy'         => 'tax_1',
			'terms'            => array( 'tax_1_term_1', 'tax_1_term_2' ),
			'field'            => 'slug',
			'operator'         => 'IN',
		),
	),
	array(
		'relation' => 'OR',
		array(
			'taxonomy'         => 'tax_1',
			'terms'            => array( 'tax_1_term_1', 'tax_1_term_2' ),
			'field'            => 'slug',
			'operator'         => 'IN',
		),
	),
);