NCic.metasenv -> NCic.context ->
[ `WithType of NCic.term | `Term | `Type | `Sort ] ->
NCic.metasenv * int * NCic.term * NCic.term (* menv,metano,instance,type *)
NCic.metasenv -> NCic.context ->
[ `WithType of NCic.term | `Term | `Type | `Sort ] ->
NCic.metasenv * int * NCic.term * NCic.term (* menv,metano,instance,type *)