private void toString(StringBuilder acc,int prec,boolean expand){
  if (this.meta != null && !expand) {
    acc.append(this.meta);
    return;
  }
  boolean paren=op.getPrec() < prec;
  if (paren)   acc.append('(');
  toString(acc,expand);
  if (paren)   acc.append(')');
}

private void toString ( StringBuilder acc , int prec , boolean expand ) { if ( this . meta != null && ! expand ) { acc . append ( this . meta ) ; return ; } boolean paren = op . getPrec ( ) < prec ; if ( paren ) acc . append ( '(' ) ; toString ( acc , expand ) ; if ( paren ) acc . append ( ')' ) ; }
this handles adding parens , as necessary .
