1 This implies that the other two sides are of equal length, and that the diagonals are of equal length. 2  An alternative definition is: a quadrilateral with an axis of symmetry bisecting one pair of opposite sides. 3  Trapezium (NAm.): no sides are parallel.
An enumeration date commonly refers to the official or control date set for a particular enumeration event such as a census. The official enumeration date may vary from one enumeration to the next. The enumeration date is a control function for collecting data over a broad space of time. All data collected is based on its validity as of a single date, no matter what date the information is taken within the enumeration period.
In this case an enumeration may be defined as follows: 1  As a bijective mapping from S to an initial segment of the natural numbers. 2  This definition is especially suitable to combinatorial questions and finite sets; then the initial segment is {1,2,..., n } for some n which is the cardinality of S.n some contexts, such as enumerative combinatorics, the term enumeration is used more in the sense of counting â with emphasis on determination of the number of elements that a set contains, rather than the production of an explicit listing of those elements.