When a word ends in a double consonant the last consonant is dropped.,
As गोमान्, यवमान्, कृतवान् and हतवान् ॥ In श्रेयान्, भूयान्, the रु though subsequent in order, does not prevent the operation of this rule, because it is asiddha 8.2.66. Thus श्रेयस् + स् = श्रेयन्स् + स् 7.1.70, = श्रेयन्स् 6.1.68 = श्रेयन्र् 8.2.66 = श्रेयन् 8.2.23 = श्रेयान् 6.4.8. But though the रुत्व does not debar lopa, it debars the जश् change. By 8.2.39, the final स् required to be changed to a letter of जश् class; रु prevents it. As यशः, पयः ॥
For रुत्व is ordained even where the present संयोगान्तलोप applies and where it does not apply. Thus it is ordained in श्रेयन्र् where the present sutra applies, as well as पयर् where this sutra does not apply. But the जश्त्व rule 8.2.39 covers the whole ground of रुत्व, hence if जश्त्व rule were not debarred by रुत्व, the latter would find no scope. Therefore रुत्व debars जश्त्व to justify its existence, but it does not debar संयोगान्तलोपः for it still has scope left to it else where.
In दध्यत्र and मध्वत्र formed from दधि + अत्र and मधु + अत्र, by changing इ and उ to य् and व्, we have दध्य् + अत्र and मध्व् + अत्र, where य् and व् are final in a pada, and so they require to be elided. It is, however, not done, because यण् substitution is a Bahiranga operation, as it depends upon two words and consequently, is considered asiddha for the purposes of this rule, which depends on one word only.
Why do we say 'of a Pada'? Observe गोमन्तौ, गोमन्तः ॥,