g'-expression

 The main problem comes from f-select expression. In current function, if the input template of f-expression doesn't contain the pattern like {edge:$variable} then occurred the error.
      [f] select $db => error.
 Template contains pair case, such as:
      [f] select {view:$db1} where {db:$db1} in $db => ok.
 I need to test more with the case:
      [f] select {view:$db1, test:$db1} where {db:$db1} in $db => ???
 The g-extend expression is always ok:
      [g]: extend rpp_g->$v with tg2 in $db.
      [gp]: extend rpp_gp->$u with tgp2 in $view.
 So the overview of the algorithm is:
      1. Consider the g-expression first.