code: def forward(self, x):
      f = self.backbone(x).flatten(start_dim=1)
      z = self.projection_head(f)
      p = self.prediction_head(z)
      z = z.detach()
      return z, p
  
file_path: lightly/examples/pytorch_lightning_distributed/simsiam.py
imports: import pytorch_lightning
  import torch
  import torchvision
  from torch import nn
  from lightly.loss import NegativeCosineSimilarity
  from lightly.models.modules import SimSiamPredictionHead, SimSiamProjectionHead
  from lightly.transforms import SimSiamTransform
label_desc: Use image node_id 2 for calling the SimSiam obj's underlying member method code with example usage: obj.forward(x) and returns: z,  p