docstr: (Internal) Create a unary-operator node.
docstr_tok: ["(","Internal",")","Create","a","unary-operator","node","."]
code: def _unary(self, expr):
      """
      (Internal) Create a unary-operator node.
      """
      e = Expression(Prio.UNARY, "minus", expr)
      d, e = e._simplify_minus()
  
      self.count_nodes += 1 + d
      return e
  
imports: import random
label_desc: Use image node_id 2 for calling the EquationGenerator obj's underlying member method code with example usage: obj._unary(expr) and returns: e