anchor.diff:  
   Zipperposition supports several input formats:
   
  -- TSTP (fof, cnf, tff)
  +- TPTP (fof, cnf, tff)
   - https://tip-org.github.io/[TIP]
   - its own native input, extension `.zf` (see directory `examples/`)
   
  
positive.code: disjunction:: `a || b`
  negation:: `~ a`
  equality:: `a = b`
  disequality:: `a != b` (synonym for `~ (a == b)`)
  implication:: `a => b`
  equivalence:: `a <=> b`
  
  
negative.code: 
  The recommended way to install Zipperposition is through http://opam.ocaml.org/[opam].
  You need to have GMP (with headers) installed (it's not handled by opam).  Once
  you have installed GMP and opam, type:
  
  ----
  $ opam install zipperposition
  