code: def valid(expr):
      """
      Check validity of a propositional sentence.
      A valid propositional sentence is True under every assignment.
  
      Examples
      ========
  
      >>> from sympy.abc import A, B
      >>> from sympy.logic.inference import valid
      >>> valid(A | ~A)
      True
      >>> valid(A | B)
      False
  
      References
      ==========
  
      .. [1] https://en.wikipedia.org/wiki/Validity
  
      """
      return not satisfiable(Not(expr))
  
imports: from sympy.logic.boolalg import And, Not, conjuncts, to_cnf, BooleanFunction
  from sympy.core.sorting import ordered
  from sympy.core.sympify import sympify
  from sympy.external.importtools import import_module
label_desc: Use image node_id 3 for calling a global function with example usage: valid(expr) and returns: unknown