add doc for ackermannize

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/ackermannization/ackermannize_bv_tactic.h

@@ -11,7 +11,37 @@ Author:
 
 Mikolas Janota
 
-Revision History:
+Tactic Documentation:
+
+## Tactic ackernannize_bv
+
+### Short Description
+
+A tactic for performing Ackermann reduction for bit-vector formulas
+
+### Long Description
+
+The Ackermann reduction replaces uninterpreted functions $f(t_1), f(t_2)$
+by fresh variables $f_1, f_2$ and addes axioms $t_1 \simeq t_2 \implies f_1 \simeq f_2$.
+The reduction has the effect of eliminating uninterpreted functions. When the reduction
+produces a pure bit-vector benchmark, it allows Z3 to use a specialized SAT solver.
+
+### Example
+
+```z3
+(declare-const x (_ BitVec 32))
+(declare-const y (_ BitVec 32))
+(declare-fun f ((_ BitVec 32)) (_ BitVec 8))
+
+(assert (not (= (f x) (f y))))
+(apply ackermannize_bv)
+```
+
+### Notes
+
+* does not support proofs, does not support unsatisfiable cores
+
+
 --*/
 
 #pragma once