Description: Konig's Theorem. If m ( i ) ~< n ( i ) for all i e. A , then
sum_ i e. A m ( i ) ~< prod_ i e. A n ( i ) , where the sums and
products stand in for disjoint union and infinite cartesian product.
The version here is proven with unions rather than disjoint unions for
convenience, but the version with disjoint unions is clearly a special
case of this version. The Axiom of Choice is needed for this proof, but
it contains AC as a simple corollary (letting m ( i ) = (/) , this
theorem says that an infinite cartesian product of nonempty sets is
nonempty), so this is an AC equivalent. Theorem 11.26 of
TakeutiZaring p. 107. (Contributed by Mario Carneiro, 22-Feb-2013)