logical connective: bridi-tail afterthought biconditional/iff/if-and-only-if.

- gigdo
- x
_{1}is a billion [British milliard] [10^{9}] of x_{2}in dimension/aspect x_{3}(default is units).

- jetydu'i
- x
_{1}and x_{2}have the same truth value; either both or none of x_{1}and x_{2}is true