code: def alpha(self, x, l, t, u):
      if u < 0:
          return 0.0
      if t == 0:
          if u == 0:
              return x[0][self.blank_symbol]
          elif u == 1:
              return x[0][l[1]]
          else:
              return 0.0
      elif l[u] == self.blank_symbol or l[u] == l[u - 2]:
          return x[t][l[u]] * (
              self.alpha(x, l, t - 1, u - 1)
              + self.alpha(x, l, t - 1, u)
          )
      else:
          return x[t][l[u]] * (
              self.alpha(x, l, t - 1, u - 2)
              + self.alpha(x, l, t - 1, u - 1)
              + self.alpha(x, l, t - 1, u)
          )
  
imports: import math
  import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
label_desc: Use image node_id 2 for calling the CTCTestBase obj's underlying member method code with example usage: obj.alpha(x, l, t, u) and returns: int, x, unknown, unknown, x, int