old_contents: '''models
  
  SUMMARY OF APIs
  multiclass(num_inputs, num_classes):
      gradient_loss(theta, x, y, probs) --> vector, number
      predict(theta, x) --> probs
  ols(num_inputs):
      gradient(theta, x, y, [prediction]) -> vector
      loss(theta, x, y, [prediction])     -> number
      predict(theta, x)                   -> number
  ridge(num_inputs, regularizer_weights):
      gradient(theta, x, y, [prediction]) -> vector
      loss(theta, x, y, [prediction])     -> number
      predict(theta, x)                   -> number
  '''
  import model_multiclass
  multiclass = model_multiclass.multiclass
  
  import model_ols
  ols = model_ols.ols
  
  import model_ridge
  ridge = model_ridge.ridge
  
new_contents: '''models
  
  SUMMARY OF APIs
  multiclass(num_inputs, num_classes):
      gradient_loss(theta, x, y, probs) --> vector, number
      predict(theta, x) --> probs
  linear(l1, l2):
      gradient(theta, x, y [,prediction]) -> vector
      loss(theta, x, y [,prediciton])     -> number
      predict(theta, x)                   -> number
  '''
  from model_linear import linear
  from model_multiclass import multiclass
  
subject: replace osl and ridge with linear