/* Provide various operations on values (Create new expressions from old ones) */
/* These could probably be made externally accessible (it would be useful) */
value add(value, value);                /* add values */
value sub(value, value);                /* ... */
value mult(value, value);
value div(value, value);
value topow(value, value);
value apply_func(FUNCTION, value);      /* Apply function to value */
value id(value);                        /* Duplicate value */
value cst(double);                      /* Create a constant expression */
value dup_var(variable *);              /* Make an expression of the form 'x' */
value dup_op(value, value, value);      /* Create an expression of type a /+-* b */
int   same(value, value);               /* Are two expressions identical ? */