anchor.diff:  disjunction:: `a || b`
   negation:: `~ a`
   equality:: `a = b`
  -disequality:: `a != b` (synonym for `~ (a == b)`)
  +disequality:: `a != b` (synonym for `~ (a = b)`)
   implication:: `a => b`
   equivalence:: `a <=> b`
   
  
positive.code: 
  Zipperposition supports several input formats:
  
  - TSTP (fof, cnf, tff)
  - https://tip-org.github.io/[TIP]
  - its own native input, extension `.zf` (see directory `examples/`)
  
  
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
  