is mentioned by

Def col_subst2(c;r) == col_map_subst(as.rel_subst2(as;r); < zip(rel_primed_vars(r);s) | s col_list_prod(map(c;rel_primed_vars(r))) > )	[col_subst2]
Def col_subst(c;r) == col_map_subst(as.rel_subst(as;r); < zip(rel_vars(r);s) | s col_list_prod(map(c;rel_vars(r))) > )	[col_subst]

In prior sections: mb collection

Try larger context: GenAutomata