Gappa Coq tactic fails if it is embedded into an imported tactic and Gappa_tactic is not importet when this outer tactic is used
When the gappa tactic is embedded into another tactic in a separate file/module which does not export Gappa_tactic and if this file is used in another file which imports this module, the gappa tactic fails with
The reference simplify was not found in the current environment.
This can be fixed by importing Gappa_tactic into the file which uses the tactic which embeds gappa, or be exporting Gappa_tactic from the file which defined the tactic.