Description: Define the "decimal constructor", which is used to build up "decimal
integers" or "numeric terms" in base 1 0 . For example,
( ; ; ; 1 0 0 0 + ; ; ; 2 0 0 0 ) = ; ; ; 3 0 0 01kp2ke3k .
(Contributed by Mario Carneiro, 17-Apr-2015)(Revised by AV, 1-Aug-2021)