Options for sledgehammer:

  * prover=NAME: name of the external prover to call
  * keep=PATH: path where to keep temporary files created by sledgehammer 
  * full_types: enable full-typed encoding
  * minimize: enable minimization of theorem set found by sledgehammer
  * minimize_timeout: timeout for each minimization step
  * metis: apply metis with the theorems found by sledgehammer
