text: from copulas.bivariate.base import Bivariate, CopulaTypes
  from copulas.bivariate.clayton import Clayton
  from copulas.bivariate.frank import Frank
  from copulas.bivariate.gumbel import Gumbel
  
  __all__ = (
      'Bivariate',
      'Clayton',
      'CopulaTypes',
      'Frank',
      'Gumbel'
  )
  