The affix tyakan comes in the sense of 'nearness' and after the words 1. upa and 2. adhi , respectively, the words so formed being Names.,
Thus उपत्यका = पर्वतस्थासन्नम् 'lowland, a land at the foot of the mountain', अधित्यका = पर्वतस्यारूढम् 'a table-land, high-land'. The rule 7.3.44 does not apply here, so we do not get the forms उपत्यिका or अधित्यिका ॥,