This option is used to define the naming scheme of the PostScript output files. The character % can be used within the option string to mark the position of the variable named parts (G001..Gn and D001..Dn, respectively).
The number of produced files depends on the specific collage grammar. G001 contains the output of the axiom in the grammar context whereas D001 contains the output of the axiom in the derivation context. G002 to Gn contain the right hand sides of the rules of the collage grammar and D002 to Dn contain the generated collages.
/f MyCollages%.ps
This produces files named MyCollagesG001.ps, MyCollagesG002.ps, ...,
MyCollagesD001.ps, MyCollagesD002.ps etc.