∀ or ∃?

This paper shows that in some axioms regarding the mixture of random variables, the requirement that the conclusions hold for all values of the mixture parameter can be weakened by requiring the existence of only one nontrivial value of the parameter, which need not be fixed. This is the case for the independence, betweenness, and mixture symmetry axioms. Unlike the standard axioms, these weaker versions cannot be refuted by experimental methods.