Meaning and spelling of１対１で対応


In a recent email conversation, an acquaintance used the expression:

> １対１で対応するそれは、大変だね。

Although I can vaguely infer the meaning of the expression １対１で対応する
(いちたいでたいおう), I am having a hard time finding a clear definition and
description of it. All the hits in Japanese pages seem to have to do with
mathematical terms (where it'd mean something like "bijective" or "one-to-one
correspondence"), but our conversation had nothing to do with mathematics and
the person is not a particularly mathematically-inclined person, so I doubt
he'd be using it a math term for an everyday-idea... Furthermore, all the hits
I got, were without that 'で' in the middle: １対１対応する

My questions:

  * what does this expression mean _in a general context_? Where does it come from? How common/familiar is it?

  * which of the two forms is the correct one? is the 'で' form a typo, or just a less common form?

  * is the spelling of '1' as roman numeral standard practice, or just e-mail shorthand, with 一対一対応 being the preferred way to write it?




・[一対一]{いったいいち}で/[一対一]{いちたいいち}で＝二人きりで, one-to-one, person-to-person  
  
・で is not a typo. We say 「一対一で対応する。」not 「一対一対応する。」  
  
・I think both 一対一 and １対１ are equally common, but probably the former is more
formal.  
  
一対一で対応する＊＊（=仕事、役目、または「＊＊さん」等の人物名・・・？）は、大変だね。= I think ＊＊(kind of work,
position etc?) is such tough work, because you have to deal with someone
(probably your guest, client, student etc.) person-to-person. / I guess ＊＊
would be tough, because you'd have to deal with your guest/client/student etc.
person-to-person.




・[一対一]{いったいいち}で/[一対一]{いちたいいち}で＝二人きりで, one-to-one, person-to-person  
  
・で is not a typo. We say 「一対一で対応する。」not 「一対一対応する。」  
  
・I think both 一対一 and １対１ are equally common, but probably the former is more
formal.  
  
一対一で対応する＊＊（=仕事、役目、または「＊＊さん」等の人物名・・・？）は、大変だね。= I think ＊＊(kind of work,
position etc?) is such tough work, because you have to deal with someone
(probably your guest, client, student etc.) person-to-person. / I guess ＊＊
would be tough, because you'd have to deal with your guest/client/student etc.
person-to-person.

