default_prover contains the name of the current prover. Note that it can be changed by using the "set prover <string>" command.

timeout is the current time limit (in seconds) for a Why3 prover to find a proof. It can be changed with "set prover <int>".

handle ss pos ps prover_name gt runs the Why3 prover corresponding to prover_name (if given or a default one otherwise) on the goal type gt, and fails if no proof is found.