A cons is a compound object having two components, called the car and cdr. These form a dotted pair. Each component can be any object.
Specializing.
(cons{[car-typespec [cdr-typespec]]})
| car-typespec | a type specifier, or the symbol *. The default is the symbol *. |
| cdr-typespec | a type specifier, or the symbol *. The default is the symbol *. |
This denotes the set of conses whose car is constrained to be of type car-typespec and whose cdr is constrained to be of type cdr-typespec. (If either car-typespec or cdr-typespec is *, it is as if the type t had been denoted.)