الَّذِي فِي الدَّارِ أَخُوكَ
The person who is in the house is your brother.
Here «fī al-dār» functions within the relative construction introduced by «alladhī». Since a relative clause requires clausal content or its functional equivalent, the example is offered as support for an underlying verbal analysis.
A reply notes that relative clauses and ordinary predicates occupy different syntactic environments. Evidence from a relative construction does not automatically settle the analysis of every adverbial predicate.