Action:

|recursively bind "f" to closure abstraction of
| ||rebind moreover bind "n" to the given datum
| |hence
| |||give the datum bound to "n"
| ||then
| ||||check (it is 0) then give 1
| |||or
| |||||enact (application (the abstraction bound to "f") to difference(the given datum,1))
| ||||then
| |||||give it
hence
||give the abstraction bound to "f" 
|then 
||enact (application (the given abstraction) to 2)

Incomplete...