问错误:不可能建立具有无限精度变量的BDD FSM

EN

MODULE main

VAR state : { s0, s1, s2, s3 };

VAR c : integer;
VAR lim : real;

ASSIGN
 init(state) := s0;
 next(state) :=
  case
   state = s0 : s1;
   state = s1 : s2;
   state = s2 & c < lim : s2;
   state = s2 & c >= lim : s3;
   state = s3 : s1;
   TRUE : state;
  esac;

 init(c) := 0;
 next(c) := (state = s2 & next(state) = s2)?(c+1):(0);

 init(lim) := 2;
 next(lim) := (state = s3 & next(state) = s1)?(lim + 1):(lim);

INVARSPEC c < 3;
INVARSPEC c < 4;
INVARSPEC c < 5;
INVARSPEC c < 6;
INVARSPEC c < 20;

LTLSPEC G F (state = s3);