gāṅ is optionally the substitute of iṅ is the causative ṇi , when that causative takes the affix san (Desiderative) and can (Aorist).,
अधिजिगापयिषति or अध्यापिपयिषति 'he desires to teach.' The form is thus evolved : गा + णिच् = गापि 7.3.36; then by the rules already stated, we get the above form with the affix सम्. अध्यजीगपत् or अध्यापिपत् 'he taught.' The ई is changed into आ by 6.1.48. Thus इ + णिच् = आ + णिच् = आ + प् + इ = आपि. This rule applies to the desideratives of causatives and aorist of causatives.,