411 REFERENCE · Wikibooks
Discrete Mathematics/Combinatory logic
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Two of the basic principles of combinatory logic in discrete mathematics are the Sum principle and the Multiplication principle.
The sum principle holds true in a given partitioned set X where partition Xi intersected with Xj is the empty set unless i is equal to j. The principle states that in such a partitioned set, the sum of the elements of each partition is equal to the number of elements in the set X.