title: how to check if a const in z3 is a variable or a value?
body: <p>just wondering in <a href="http://rise4fun.com/z3py" rel="noreferrer">z3py</a> , how do I check if a given constant expression is a variable or value ? For example  </p>
  
  <pre><code>x = Int('x')
  x_ = IntVal(7)
  ColorVal, (White,Black)  = EnumSort("ColorVal",["While","Black"])
  mycolor = Const("mycolor",ColorVal)
  </code></pre>
  
  <p>So x,mycolor would all be variables and x_,True,False,White,Black would be values and not variables .  </p>
  
  <p>z3py has is_var predicate but for different purpose.   This is useful if I want to rename all variables in a formula to something else.  </p>