Reason: vector in in init folder was introducing an overload (`::`) for
all Lean users. The workaround (use `local infix ::`) was
counterintuitive.
We currently have no special support for bitvectors in the code
generator. Thus, there is no need to have vector and bitvec in the init
folder right now. Moreover, the new parser and elaborator (issue #1674) should
provide better ways of managing overloaded symbols.
The issue was that instantiate_mvars(infer(m)) had a metavariable, while
infer(instantiate_mvars(m)) did not. Changing the call from assign to
is_def_eq also unifies the type, assigning the metavariable inside the
type.
This happened in Johannes' real number formalization. We tried to
unfold a noncomputable definition even though it would have been erased
afterwards, and failed.
The check_computable check was introduced in order to fix the error
message in #1401, the error message is still intelligible in that
example.
As suggested by David Chisnall. If I read the spec correctly, it would
be unsafe to use the release ordering for dec_ref_core: then the
following situation could happen:
```c++
// m_rc -> 2
// Thread 1:
unsigned x = atomic_fetch_sub_explicit(&m_rc, 1u, memory_order_release);
// Thread 2:
unsigned y = atomic_fetch_sub_explicit(&m_rc, 1u, memory_order_release);
// x = y = 1u, m_rc -> 2
```
That is, a release store operation is not required to be visible to
another release operation.
Herb Sutter also recommends the acq_rel ordering for reference counters.
This gives a workaround for the situation where the `congr` tactic does too much congruence applications, such as reducing `|- a + b = b + a` to `|- a = b` and `|- b = a`, by supplying the desired equalities to stop at using `have`.
Now tactics supporting locations can also specify the goal among the locations by using the name `⊢` or `|-`. Also `rw at *` is implemented so that it will rewrite any hypotheses or the goal for which the whole sequence of rewrites succeeds. (This is different from `rw at h1 h2 ... hn |-`, which requires that all rewrites run to completion on each specified target.)
