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