What is the usage of 有 in 有比丘五下分結盡?
有比丘五下分結盡。


有（些）比丘五下分結（已滅）盡。
有些比丘已滅盡五下分結。
Some bhiksus (Sanskrit: bhikṣu) have completely eliminated five lower-realm bonds.

此處之「下分」是指「欲界」。三界中，欲界處於最下層，低於色界、無色界，故稱之為下分。
下分 here means Realm of Sensuous Desire (Sanskrit: kāma-dhātu). It is the lowest level in the Three Realms, lower than the Realm of Form and the Realm of Formlessness. Thus, it is named 下分(界).

「結」是「繫縛」之義，亦即「煩惱」。此等煩惱繫縛眾生於三界，令吾等無止盡地輪迴，故名之為「結」。
結 (Sanskrit: saṃyojana; bandhana) here means the bond, whose alias is the affliction (Sanskrit: kleśa). The affliction fastens all beings in the Three Realms, and makes us transmigrate endlessly. Therefore, it is named 結.

五下分結 （Sanskrit: pañca-āvara-bhāgīya-saṃyojanāni, five lower-realm bonds）：
貪 (desire)
瞋 (anger; dislike)
身見：執著實我 (real self)
戒取：邪戒 (heretical precept or discipline)
疑 (doubt)