Major Section: PROGRAMMING
For any string pkg that names a package currently known to ACL2,
(pkg-witness pkg) evaluates to a symbol in that package whose
symbol-name is the value of constant *pkg-witness-name*.
(Pkg-witness pkg) has a guard of (stringp pkg). However, if
pkg-witness is called on an argument that is not the name of a package
known to ACL2, a hard Lisp error will result.