fact: Definition queens_safe3 n : M _ := do s <- get; (do rs <- perms (map Z_of_nat (iota 0 n)) ; put empty >> safe3 (place n rs) >> put s >> Ret rs).
imports: ZArith mathcomp(all_ssreflect) infotheo(ssrZ) monae_lib hierarchy monad_lib fail_lib state_lib