content := elements EOF | EOF

elements ::= element | element nls elements

element ::= itm | nls

itm ::= prf_tree | def_prf | def_fml | comment

def_prf ::= atomic_prf_tree def nls prf_tree

def_fml ::= fml def fml

def ::= ':='

comment ::= '#' [! NL]*

nls ::= NL+