anchor.diff:  === Native Syntax
   
   The native syntax, with file extension `.zf`, resembles a simple fragment of
  -ML with explicit polymorphism. Every symbol must be declared, using
  -the builtin type `prop` for propositions. A type is declared
  -like this: `val i : type.` and a parametrized type: `val array: type -> type.`
  +ML with explicit polymorphism. Many examples
  +in `examples/` are written using this syntax.
  +A vim https://github.com/c-cube/vim-zf[syntax coloring file] is available.
  +
  +
  +==== Basics
  +
  +Comments start with `#` and continue to the end of the line.
  +Every symbol must be declared, using the builtin type `prop` for propositions.
  +A type is declared like this: `val i : type.`
  +and a parametrized type: `val array: type -> type.`
   
   ----
   val i : type.
  
positive.code: for proving `false`. Indeed, proving `a ⇒ b` is equivalent to deducing
  `false` from `a ∧ ¬b`.
  
  A handy way of displaying the proof is to use http://graphviz.org/[graphviz]:
  
  ----
  
negative.code: ----
  
  image::doc/example_proof.svg[alt="simple proof graph",link="doc/example_proof.svg"]
  
  === Proof Format
  
  It is possible to avoid displaying the proof at all, by using `-o none`.
  A TSTP derivation can be obtained with `-o tstp`.
  
  
  === Library
  