षात् पदान्तात्

Thus निष्पानम्, दुष्पानम्; the visarga is changed to ष् here by 8.3.41. The rule 8.4.29 is debarred. सर्पिष्पानम् (is a genitive compound contra 2.2.14). So also यजुष्पानम् 2.1.32. The ष is in these two by 8.3.45, and 8.4.10 is debarred.

Why do we say \षात् after a ष्?\ Observe निर्णयः ॥

Why do we say पदान्तात् 'final in a Pada'? Observe कुष्णाति, पुष्णाति ॥ The word पदान्त is equivalent to पदे अन्त or Locative Tatpurusha; and does not mean final of a Pada. Therefore the rule does not apply here. सुसर्पिष्केण (instrumental singular) सुयजुष्केण ॥ Here the क is added by 5.4.154. शोभनं सर्पिरस्य = सुसर्पिष्क (a Bahuvrihi). The ष is by 8.3.39. Before the affix क, the word सुसर्पिस् is a Pada (1. 4. 17), and thus स् (ष्) is final of a Pada: but it is not final of a preceding member followed by another Pada. The rule, in fact, applies to compounds, the ष् being final in the first term.,