दो दद् घोः

As दत्तः, दत्तवान्, दत्तिः ॥ Why of दा? Observe धीतः, धीतवान् from घेट् : and the long ई is by 6.4.66. Why when it is a Ghu? Observe दातं बर्हिः from दाप् 'to cut', and अवदातं मुखं from दैप् 'to cleanse', The substitute is दथ् ending in थ, according to an Ishti.

Karika:-

तान्ते दोषो दीर्घत्वं स्वाद्, दान्ते दोषो निष्ठा नत्वम् ।
धान्ते दोषो धत्व प्राप्तिम्, थान्तेऽदोषस्तस्मात् थान्तम् ॥

If the substitute be दत् ending in त्, then it would require the lengthening taught in 6.3.124 (N. B. The sutra should be interpreted as 'the vowel of the Preposition is lengthened before a substitute of क्ष which ends in त्', in order to make this objection applicable. That sutra however is capable of another interpretation). If the substitute be दद् ending in द् then the Nishtha त would be changed to न by 8.2.42: as in भिद् + त = भिन्नः ॥ If the substitute be दध् ending in ध्, then by 8.2.40; the Nishtha त would be changed to ध ॥ Hence the substitute is दथ् ॥ If however, the sutra 6.3.124, is interpreted as \the vowel of a preposition is lengthened before a substitute of दा which begins with त्\, then the substitute may be दत् also without any harm. Even if the substitute be दद् or दध्, the apprehended न् and ध् substitutions will not take place, on the maxim सन्निपातलक्षणो विधिरनिमित्तं तद्विघातस्य ॥

The following are exceptions to 7.4.47, अवदत्तं, विदत्तं, प्रदत्तं, सुदत्तं, अनुदत्तं and निदत्तं ॥ Or the words अव &c, here are not Upasargas. See 1.4.57.

Karika:-

अवदत्तं विदत्तं च प्रदत्तं चादिकर्म्मणि ।
सुदत्तमनुदत्तं च निदत्तमिति चेष्यते ॥

The word आदिकर्मणि qualifes pradatta only. The word च shows that regular forms अवत्तं, वित्तं, प्रत्तं, &c also are valid.,