private function needsCompilation($lessPath, $cssPath)
	{
		/**
		 * Checks whether $subject has been modified since $reference was
		 */
		$isNewer = function($subject, $reference) {
			return filemtime($subject) > filemtime($reference);
		};

		// Check for obvious cases
		if ($this->forceCompile || !file_exists($lessPath) 
				|| !file_exists($cssPath) || $isNewer($lessPath, $cssPath))
		{
			return true;
		}

		// Finally, check if any imported file has changed
		return $this->checkImports($lessPath, $cssPath, $isNewer);
	}