`declaim` is just as implementation-dependant as the :type specifiers for defstruct, thus by lispm's rules, there are no 'standard' ways to apply type conditions.
But then, the standard /is/ useless.
But then, the standard /is/ useless.
There are implementations which check these type constraints. So it is best to check the manual or ask the maintainers. IIRC there were implementations which added it on user requests.
But don't think all "Common Lisp" implementations will check those constraints, for example ABCL does not. Some don't and in others it can be turned off.