Remark
19
[01M] This wording is commonly used: ”let \(I\) be a non-empty set of indices, and \(A_ i\) a family of setsCDLeng indexed by \(i∈ I\)”; this, in axiomatic theory, should be written as ”let \(I\) be a non-empty set, let \(X\) be a set, and \(A:I→{\mathcal P}(X)\) a function; we will write \(A_ i\) instead of \(A(i)\)”. (With this writing we have that \(A_ i\) are all subsets of \(X\)).