Irish: To Have to Do Something in Relative Clauses
If ...
the man who has to buy her another book
=an fear a bhfuil air leabhar eile a cheannach di
should...
the book that the man has to buy (for) her
be,
1. an leabhar atá ar an bhfear a cheannach di
or
2. an leabhar atá ar an bhfear cheannach di