  We study the computational complexity of universality and inclusion problems
for unambiguous finite automata and context-free grammars. We observe that
several such problems can be reduced to the universality problem for
unambiguous context-free grammars. The latter problem has long been known to be
decidable and we propose a PSPACE algorithm that works by reduction to the
zeroness problem of recurrence equations with convolution. We are not aware of
any non-trivial complexity lower bounds. However, we show that computing the
coin-flip measure of an unambiguous context-free language, a quantitative
generalisation of universality, is hard for the long-standing open problem
SQRTSUM.
