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<?php

$arResult['NAV_RESULT_NAV_NUM'] = $arResult['NAV']->NavNum;

$arResult['NAV_RESULT_NAV_PAGE_NOMER'] = $arResult['NAV']->NavPageNomer;

$arResult['NAV_RESULT_NAV_PAGE_COUNT'] = $arResult['NAV']->NavPageCount;

$arResult['SECTION_SECTION_PAGE_URL'] = !empty($arResult['SECTION']['SECTION_PAGE_URL']) ? $arResult['SECTION']['SECTION_PAGE_URL'] : null;

$cacheResultKeys = array_merge(
    $cacheResultKeys,
    [
        'NAV_RESULT_NAV_NUM',
        'NAV_RESULT_NAV_PAGE_NOMER',
        'NAV_RESULT_NAV_PAGE_COUNT',
        'SECTION_SECTION_PAGE_URL',
    ]
);

<?php
if (
    isset($arResult['NAV_RESULT_NAV_NUM'], $arResult['NAV_RESULT_NAV_PAGE_NOMER'], $arResult['SECTION_SECTION_PAGE_URL'])
    && (
        array_key_exists('PAGEN_' . $arResult['NAV_RESULT_NAV_NUM'], $_GET)
        || $arResult['NAV_RESULT_NAV_PAGE_NOMER'] > 1
    )
) {
    $APPLICATION->SetPageProperty('canonical', 'http://' . $server->getHttpHost() . $arResult['SECTION_SECTION_PAGE_URL']);
}

if (
isset(
    $arResult['NAV_RESULT_NAV_NUM'],
    $arResult['NAV_RESULT_NAV_PAGE_NOMER'],
    $arResult['NAV_RESULT_NAV_PAGE_COUNT'],
    $arResult['SECTION_SECTION_PAGE_URL']
)
) {
    $paramName = sprintf('PAGEN_%s', $arResult['NAV_RESULT_NAV_NUM']);

    if ($arResult['NAV_RESULT_NAV_PAGE_COUNT'] > $arResult['NAV_RESULT_NAV_PAGE_NOMER']) {
        // next
        $urlNextRel = htmlspecialcharsbx(
            CHTTP::urlAddParams(
                CHTTP::urlDeleteParams(
                    $arResult['SECTION_SECTION_PAGE_URL'],
                    $paramName,
                    [
                        'delete_system_params' => true
                    ]
                ),
                [
                    $paramName => $arResult['NAV_RESULT_NAV_PAGE_NOMER'] + 1,
                ],
                [
                    'skip_empty' => true,
                ]
            )
        );
    }

    if ($arResult['NAV_RESULT_NAV_PAGE_NOMER'] > 1) {
        // prev
        $urlPrevRel = htmlspecialcharsbx(
            CHTTP::urlAddParams(
                CHTTP::urlDeleteParams(
                    $arResult['SECTION_SECTION_PAGE_URL'],
                    $paramName,
                    [
                        'delete_system_params' => true
                    ]
                ),
                [
                    $paramName => (
                    ($arResult['NAV_RESULT_NAV_PAGE_NOMER'] - 1) == 1
                        ? ''
                        : $arResult['NAV_RESULT_NAV_PAGE_NOMER'] - 1
                    ),
                ],
                [
                    'skip_empty' => true,
                ]
            )
        );

    }

    if (isset($urlNextRel)) {
        $APPLICATION->SetPageProperty('next', 'http://' . $server->getHttpHost() . $urlNextRel);
    }

    if (isset($urlPrevRel)) {
        $APPLICATION->SetPageProperty('prev', 'http://' . $server->getHttpHost() . $urlPrevRel);
    }

}

https://www.olegpro.ru/post/1s_bitriks_kastomnye_kanonicheskie_urly__relprev_i_relnext.html

<?php
$APPLICATION->AddBufferContent([$APPLICATION, 'GetLink'], 'prev');
$APPLICATION->AddBufferContent([$APPLICATION, 'GetLink'], 'next');