There is an interesting comment by Dr. Avinash Sathaye. It is self-explanatory and is hence quoted below verbatim –
नमो नमः !
You wrote: २.२३ प्रति-उद्यमः “प्रति + उत् + यम्” १ प. (= to undertake) इति धातुः । तस्मात् क्रियावाचकम् पुल्लिङ्गि नाम “प्रत्युद्यम” (= undertaking) । तस्य प्रथमा विभक्तिः एकवचनम् च । I would suggest a different split: कूपखननं प्रति उद्यमः -effort towards digging a well. Thus, I would use प्रति like an adverb. I don’t recall seeing प्रति + उद् +यम् with such a meaning. If you know its use elsewhere, I would like to know. *
My comments on the observation by Dr. Sathaye is –
* I considered प्रति as an उपसर्ग as in प्रतिकार. Since प्रतिकार means “counter-action” प्रत्युद्यमः can also mean “counter of उद्यमः” Accordingly प्रत्युद्यमः answers inherently the question कीदृशः उद्यमः ?
Admittedly however, interpretation deriving from taking प्रति to be an independent word, an adverb makes the interpretation very straightforward. Thank you Dr. Sathaye !
संस्कृताध्ययनम् । 