Proof_usingSourceUtility code for section variables handling in Proof using...
At some point it would be good to make this abstract
val definition_using :
Environ.env ->
Evd.evar_map ->
fixnames:Names.Id.t list ->
using:Vernacexpr.section_subset_expr ->
terms:EConstr.constr list ->
tProcess a using expression in definitions to provide the list of used terms
For the stm