In[]:=
dec=NetDecoder[{"Class",{"a","b","c"}}]​​NNcompare=NetChain[{LinearLayer[3],ElementwiseLayer[LogisticSigmoid],LinearLayer[3],ElementwiseLayer[LogisticSigmoid],LinearLayer[3],ElementwiseLayer[LogisticSigmoid],LinearLayer[3],SoftmaxLayer[],dec}]
Out[]=
NetDecoder
Type:
Class
Input:
vector(size: 3)
​

NetChain
:NetDecoder[Class,Labels{a,b,c},InputDepth1,MultilabelFalse,Dimensions3,$Rank0,$Version13.3.0,NeuralNetworks`TensorT[{3},NeuralNetworks`AtomT]] is not a layer, a net, or a valid specification for one.
Out[]=
$Failed