The nasal above the roots (i.e. anudātta ending in a nasal and vana and tanādi) is optionally elided before the Absolutive affix lyap,
This is a vyavasthita-vibhasha. The option applies to roots ending in म्. In the case of roots ending in other nasals, the elision is compulsory. Thus प्रयत्य or प्रयम्य, प्ररत्य or प्ररम्य, प्रणत्य or प्रणम्य, आगत्य आगम्य, but no option in आहत्य, प्रमत्य, प्रवत्य, प्रक्षत्य ॥,