Def  k!m ==  i:{k-m..k}. i+1

is mentioned by

Thm*  (a inj b) ~ (b!a)

[nsub_inj_factorial_tail]

In prior sections: IteratedBinops

Try larger context: DiscrMathExt IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html