The function new_definition provides a facility for definitional extensions.
It takes a term giving the desired definition. The value returned by
new_definition is a theorem stating the definition requested by the user.
Let v_1,...,v_n be tuples of distinct variables, containing the variables
x_1,...,x_m. Evaluating new_definition `c v_1 ... v_n = t`, where c is a
variable whose name is not already used as a constant, declares c to be a new
constant and returns the theorem:
|- !x_1 ... x_m. c v_1 ... v_n = t
Optionally, the definitional term argument may have any of its variables
universally quantified.
FAILURE CONDITIONS
new_definition fails if c is already a constant or if the definition does
not have the right form.
EXAMPLE
A NAND relation on signals indexed by `time' can be defined as follows.
# new_definition
`NAND2 (in_1,in_2) out <=> !t:num. out t <=> ~(in_1 t /\ in_2 t)`;;
val it : thm =
|- !out in_1 in_2.
NAND2 (in_1,in_2) out <=> (!t. out t <=> ~(in_1 t /\ in_2 t))
COMMENTS
Note that the conclusion of the theorem returned is essentially the same as the
term input by the user, except that c was a variable in the original term but
is a constant in the returned theorem. The function define is significantly
more flexible in the kinds of definition it allows, but for some purposes this
more basic principle is fine.