(* example of incorrect set of productions *)

   EBNF = { Production } .

   Production = nonterminal "=" Expression "."  .

   Expression = Term { "|" Term  .  (*  missing closing } *)

   Term = Factor { %%% Factor } .   (* includes invalid characters *)

   Factor =
          nonterminal
          | terminal
          | "[" Expression "]"
          | "(" Expression ")" )    (* has spurious closing ) *)
          | "{" Expression "}" .