There is vocalisation of the half-vowel of the reduplicate of dyut and svāpi (Causative of svap).,
As वि विद्युतत्, वि विद्योतिषते, वि विद्युतिषते, 1.2.26 वि देद्युत्यते ॥ स्वापि-सुष्वापयिषति ॥ The Causative of स्वप् is taken here, and the vocalisation takes place then only, when it is immediately followed by an affix which causes reduplication. Therefore not here, स्वापि + ण्वुल् = स्वापकः; स्वापक + क्यच् = स्वापकीय, स्वापकीय + सन् = सिष्वापकीयिषति ॥
The simple root स्वप् will get vocalised in its reduplicate by 6.1.15, 6.1.17 in the Perfect. The Desiderative of स्वप् is कित् by 1.2.8, and therefore the reduplicate of स्वप् will be vocalised before सन् by (VI. I. 15). The reduplicate of स्वप् will be vocalised in the Intensive also by 6.1.19.
Quere:- Does the reduplicate of the Desiderative of the Denominative verb द्योतकीयति get vocalised or not.,