The elaborator was failing in the following higher-order constraint
ctx |- (?M a) = (?M b)
This constraint has solution, but the missing condition was making the elaborator to reduce this problem to
ctx |- a = b
That does not have a solution.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
(optional) Boost (version >= 1.54), we can
build Lean using boost::thread instead of std::thread. When using
Boost, Lean can modify the thread stack size.