+ (* Declarative langauge *)
+ (* Not the best idea to use a string directly, an abstract type for identifiers would be better *)
+ | Assume of loc * string * nterm (* loc, identifier, type *)
+ | Suppose of loc * nterm * string (* loc, assumption, identifier *)
+ | By_just_we_proved of loc * just * nterm * string option (* loc, justification, conclusion, identifier *)
+ | We_need_to_prove of loc * nterm * string option (* loc, newconclusion, identifier *)
+ | BetaRewritingStep of loc * nterm
+ | Bydone of loc * just
+ | ExistsElim of loc * just * string * nterm * nterm * string
+ | AndElim of loc * just * nterm * string * nterm * string
+ | RewritingStep of
+ loc * nterm * [ `Term of nterm | `Auto of auto_params | `Proof | `SolveWith of nterm ] * bool (* last step*)
+ | Obtain of
+ loc * string * nterm
+ | Conclude of
+ loc * nterm
+ | Thesisbecomes of loc * nterm
+ | We_proceed_by_induction_on of loc * nterm * nterm
+ | We_proceed_by_cases_on of loc * nterm * nterm
+ | Byinduction of loc * nterm * string
+ | Case of loc * string * (string * nterm) list
+ (* This is a debug tactic to print the stack to stdout, can be safely removed *)
+ | PrintStack of loc