The function f represents a series of operations, including self-interaction, convolutional message passing, MLPs and non-linearity. In the convolution operation, the equivariant network considers the case where l max is greater than 0, while the invariant network only handles the l = 0 part. The convolutional layer L, which is used in the equivariant network to facilitate interaction with filter f acting on input u and producing output o, is denoted as o: l u l f → l o , and is defined using the following equation: 39