This is used within neurons to trigger action if none of the rules are triggered. The output action can be any function call, or in/out reference to the neuron currently under processing.
(def-neuron test3
(and (in 1 'a) (in 2 'a)) ; test
'a ; fire if true
(and (in 1 'b) (in 2 'a) (out 'a -1))
'x
(otherwise '=)
)
Here otherwise picks from the in 1 pattern the current symbol.