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**: 用ゐる is a compound verb composed of 持つ (to hold) and 率る (to lead/bring along), but even its oldest attestations in Old Japanese, its conjugation class had been in flux, sometimes being seen in the upper two-grade forms 用ふ and 用ゆ up until Modern Japanese in which its upper one-grade form became standard.
**: One genre in which 用ゐる was almost always seen in its upper two-grade form was 漢文訓読（※）. In this genre, there were a handful of other verbs with altered verb classes. Another such example is 試みる, which could be seen as an upper two-grade verb as 試む. 

※"Kanbun Kundoku" as it is even referred to in English is the literary creole language between Japanese and Classical Chinese which preserved the semantic choices in Kanji of Classical Chinese while being altered to fit Japanese syntax.

The name "upper one-grade" comes from the fact that their vowel-ending stems end in/i/, which is a 'high' vowel in phonetics. The -ru (終止形・連体形), -re (已然形), and -yo (命令形) seen in their respective bases are affixes used to create them. 

1. 春は藤波(ふぢなみ)を見る。（終止形）
In spring, one looks at the waves of wisteria.
From the 方丈記.

2. 月な見給ひそ。（連用形＋給ふ）
Don't look at the moon.
From the 竹取物語.

3. 又、いさゝか覚束なくおぼえて、頼むにもあらず、頼まずもあらで、案じゐたる人あり。（連用形＋たり）
Moreover, there are those who are somewhat doubtful, neither trusting nor not trusting, who ponder.

From the 徒然草.

4. まして、明らかならん人の、惑へる我等を見んこと、掌の上の物を見んが如し。（未然形＋ん）
To say nothing of it, a clear-headed person trying to look at bewildered people such as ourselves would be no different than trying to look at something in the palm of their hands. 

From the 徒然草.

5. 魚(いを)と鳥とのありさまを見よ。（命令形）
Look at how the fish and birds are.
From the 方丈記.

6. その澤のほとりの木の陰に下り居て、 餉（かれいひ）食ひけり。（連用形＋て）
They got off (their horses) and sat down in the shade of a tree on the edge of the marsh, where they then ate some dried rice.
From the 伊勢物語.

7. 同じき四日、病（やまひ）に責められ、せめての事に板に水をいて、それに伏し転（まろ）び給へども、助かる心地もし給はず。（連用形＋て）

On the fourth day of the same (month), while plagued by illness, he tried to at least dowse the floor with water and laid down, but not even this felt like it helped.
From the 平家物語．

8. あまりに供米の不法にて、ただ糠(ぬか)のみ多く候へば、それをひさせむとて置きたるものをば、いかでか取り捨て候ふべき。（未然形＋さす）
Why should you through out rice put down to sift out excess bran just because it had too much stuck in it to be used as an offering?  
From the  古今著聞集．

9.   消えかへり露もまだひぬ袖の上に今朝はしぐるる空もわりなし。（未然形＋ず）

This morning, the sky has no way to dispel the rain though my sleeves have yet to dry even a drop of my tears, having (spent the night)  feeling as if my soul were fading. 
From the 蜻蛉日記.