if( allEmpty ) { cs.clear(); cs.append(make.Sequence(choices[0].pos, Tree.EMPTY_ARRAY)); }
    TreeList flattenAlternativeChildren( Tree[] choices ) {	TreeList cs = new TreeList();	for( int j = 0; j < choices.length; j++ ) {	    Tree tree = flattenAlternative( choices[ j ] ); // flatten child	    switch( tree ) {	    case Alternative( Tree[] child_choices ):		appendNonEmpty( cs, child_choices );		break;	    default:		appendNonEmpty( cs, tree );	    }	}	//System.out.println( cs.length() );	return cs;    }