The general rule for this can expressed as:
where n some number of possibilities.
This basically states that we can take n possible events and us f to generate as single possible outcome.
This extends set membership since we could have varying definitions of, say, hot curries. One person might declare that only curries of Vindaloo strength or above are hot whilst another might say madras and above are hot. We could allow for these variations definition by allowing both possibilities in fuzzy definitions.