How to deal with the error that Nusmv cannot check ctl properties with input variables (IVAR)?

Question

MODULE main

IVAR v1 ：boolean;

VAR v2 : boolean;

SPEC NAME p1 := AG (v1&v2);

file ltlerror.smv: line 8: Property contains input variables:

Answer 1

At pages 24-25 of NuSMV 2.6 user manual, it's written:

[...] input variables cannot occur in:

[...]

• Some specification kinds: CTLSPEC, SPEC, INVARSPEC, COMPUTE, PSLSPEC. For example:

  IVAR i : boolean;
  VAR s : boolean;
  SPEC AF (i -> s) – this is NOT allowed 
  LTLSPEC F (X i -> s) – this is allowed
  

---

Workarounds:

1. use LTL:

   MODULE main
   IVAR
     v1 : boolean;
   VAR
     v2 : boolean;
   
   LTLSPEC NAME p1 := G (v1 & v2);
   

2. Declare v1 as a normal variable, but use it as an input variable. To do this, do not impose any constraint on the initial and future values of v1, i.e. do not write init(v1) := or next(v1) := or equivalent constraints.