③苇大 First集 The first set of a sequence of symbols u, written as First(u) is the set of terminals which start all the sequences of symbols derivable from u. a bit more formally, consider all strings derivable from u by a leftmost derivation If u=*v, where v begins with some terminal, that terminal is in First(u). Ifu=>*8 then s is in First(u)The first set of a sequence of symbols u, written as First(u ) is the set of terminals which start all the sequences of symbols derivable from u. A bit more formally, consider all strings derivable from u by a leftmost derivation. If u =>* v , where v begins with some terminal, that terminal is in First(u). If u =>*  , then  is in First(u ). First 集