Meaning of 誰もいはしない in this sentence

Question

どうせ誰もいはしないと高をくくっていたところもある。

This one's throwing me for a bit of a loop. The translation says "He also didn't really take the possibility of anyone being there seriously."

It makes sense to me except for the いはしない part. What does this mean?

I looked up い and saw that it can mean stomach, so my first thought was that いはしない was perhaps some idiom like "not doing his stomach" that means "not being there" but I can't find any evidence to justify that on the internet so I have to assume it's wrong.

Answer 1

「Verb in 連用形{れんようけい}(continuative form) +は + しない」

= "would not (verb)" ← rather emphatic

「い」 is the 連用形 of the verb 「いる」.

「誰{だれ}もいはしない」, therefore, means "no one would be (there)"

You will encounter this grammar pattern over and over.