Lash is a higher-order automated theorem prover created as a
  fork of the theorem prover Satallax.  The basic underlying calculus
  of Satallax is a ground tableau calculus whose rules
  only use shallow
  information about the terms and formulas taking part in the rule.
  Lash uses new, efficient C representations of vital
  structures and operations. Most importantly, Lash uses a C
  representation of (normal) terms with perfect sharing along with a C
  implementation of normalizing substitutions.
  We describe the ways
  in which Lash differs from Satallax and the performance improvement
  of Lash over Satallax when used with analogous flag settings.