code: def step(self, t0, t1, y0, extra0):
      del extra0
      dt = t1 - t0
      I_k = self.bm(t0, t1)
  
      f, g_prod = self.sde.f_and_g_prod(t0, y0, I_k)
  
      y0_prime = y0 + dt * f + g_prod
  
      f_prime, g_prod_prime = self.sde.f_and_g_prod(t1, y0_prime, I_k)
  
      y1 = y0 + (dt * (f + f_prime) + g_prod + g_prod_prime) * 0.5
  
      return y1, ()
  
imports: from ..None import base_solver
  from ...settings import SDE_TYPES, NOISE_TYPES, LEVY_AREA_APPROXIMATIONS
label_desc: Use image node_id 2 for calling the Heun obj's underlying member method code with example usage: obj.step(t0, t1, y0, extra0) and returns: y1,  