<?php

$dt1_1 = date("Y-m-d", strtotime(str_replace("/","-","10/05/2017")));
$dt1_2 = date("Y-m-d", strtotime(str_replace("/","-","15/05/2017")));
$dt2_1 = date("Y-m-d", strtotime(str_replace("/","-","18/04/2017")));
$dt2_2 = date("Y-m-d", strtotime(str_replace("/","-","23/10/2017")));

if(($dt1_1 <= $dt2_2) && ($dt1_2 >= $dt2_1)){
	echo "True";
}else{
	echo "False";
}