There are several slightly different sorts of collapsing algebras. If κ and λ are cardinals, then the Boolean algebra of
regular open sets of the
product space κλ is a collapsing algebra. Here κ and λ are both given the
discrete topology. There are several different options for the topology of κλ. The simplest option is to take the usual product topology. Another option is to take the topology generated by open sets consisting of functions whose value is specified on less than λ elements of λ. ==References==