### Implicit (derived from the FU set)

`max_fu_inputs` -- the maximum, across the concrete FU occurrence set, of each
FU's input-port count. If FU `f0` has 2 inputs and FU `f1` has 3 inputs,
`max_fu_inputs = 3`.

`max_fu_outputs` -- the maximum, across the concrete FU occurrence set, of each
FU's output-port count. Same shape.