116  Pascal User Manual  which are formed accordng to the E B NF below. A period terminates the  input.  Expression  =  Term  { (  "+" I "-" )  Term} .  Term  =  Factor  {  "*,,  Factor  }.  Factor  =  Identifier  "("  Expression  ")" .  Identifier  =  Letter.  program PostFix (Input,Outpu'  );  { Program 11.5 - Convert an infix expression to  Polish  I  ostfix form.  label 13 { premature end  f  file  };  var  Ch:  Char;  procedure Find;  begin  if Eof(Input)  then goto  13;  repeat  Read (Input,  Ch);  until  (Ch  <>  '  ')  or Eo: (Input)  end { Find };  procedure Expression;  var  Op:  Char;  procedure Term;  procedure Factor;  begin  if Ch  =  '  ('  then  begin  Find;  ExpJession;  {Ch  else  Write (Output,  Ch);  Find  end { Factor };  begin { Term }  Factor;  while Ch  , *,  do  , )'  }  end  begin  Find;  Facto];  Write (Output,  '*')  end  end { Term };  begin { Expression  Term;  while  (Ch = '+')  or  (Ch  =  '-')  do  begin  Op  := Chi  Find;  TE rm;  Write (Output,  Op)  end  end { Expression }; 