'Create a Problem.
Args:
was_reversed: bool, whether to reverse inputs and targets.
was_copy: bool, whether to copy inputs to targets. Can be composed with
was_reversed so that if both are true, the targets become the inputs,
which are then copied to targets so that the task is targets->targets.'

def __init__(self, was_reversed=False, was_copy=False):

    self._was_reversed = was_reversed
    self._was_copy = was_copy
    self._encoders = None
