تَحْتَ

[sinimmar]

بسم الله ارحمان ارحيم

السلام عليكم

Are the expressions تَحْتَ or خَلْفَ always مَفْتوُح ? Why does it become مكسور when they take ضَمَاءِر المتصل? What is the name or form of this rule? For example:

تحتَ اشّجرةِ = تَحْتِهاَ

[irf2k]

بسم الله ارحمان ارحيم

السلام عليكم

Do NOT confuse
تحتَ شّجرةِ
with an idafah (Mudafu + Mudafu alaihe). It an adverb (of place) plus mudafu alaihe.
All adverbs need be fallowed by a mudafu alaihe (majrur).
This combination (Zarf + Mudafu Alaihe) does not have any special name, as far as I know.