= Coeval binary population
A coeval binary has components formed at the same time. A population of such <binary stars> can still have a distribution of system ages. If component masses have <independence> and the state at age $t$ is determined separately for each component, the states have <conditional independence> given $t$. If $g(t)$ and $w(t)$ are the conditional <probabilities> of two states, the unconditional unordered pair fractions are $\mathbb E[g(t)^2]$ and $2\mathbb E[g(t)w(t)]$, not generally products of marginal state fractions.
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