old_contents: class EagerResolutionMixin(object):
      def _concrete_value(self, e):
          r = super(EagerResolutionMixin, self)._concrete_value(e)
          if r is not None:
              return r
  
          for b in backends._eager_backends:
              try:
                  return b.convert(e)
              except BackendError:
                  pass
  
          return None
      _concrete_constraint = _concrete_value
  
  from .. import backends
  from ..errors import BackendError
  
new_contents: class EagerResolutionMixin(object):
      def _concrete_value(self, e):
          r = super(EagerResolutionMixin, self)._concrete_value(e)
          if r is not None:
              return r
  
          for b in backends._eager_backends:
              try:
                  return b.eval(e, 1)[0]
              except BackendError:
                  pass
  
          return None
      _concrete_constraint = _concrete_value
  
  from .. import backends
  from ..errors import BackendError
  
subject: fix eager evaluation