In this comparison, if
P is unconstrained,
the constraints on
A are not considered
. If
P contains a template parameter pack, then
A also matches
P
if each of
A's template parameters
matches the corresponding template parameter in the
template-head of
P. When
P's
template-head contains a template parameter
pack (
[temp.variadic]), the template parameter pack will match zero or more template
parameters or template parameter packs in the
template-head of
A with the same type and form as the template parameter pack in
P
(ignoring whether those template parameters are template parameter packs)
.