Functions having this property include functions mapping sets to their closure and vector space projections.   
The number of elements in the free monoid described by this term is givenidentify this set of numbers of the form a + bı where ı = Answer: complex numbers n  n  k    2iby k (k − i + 1) . Numbers are said to be this if they are expressible k=0 i=1 n  n−kintheform k k ;thisisbecausethesumfromk=0tonofsuchnumbersgives the number of functions with this property on a set with n elements. Functions having this property include functions mapping sets to their closure and vector space projections.   Absorbing elements have this property for the binary operations under which they absorb; and identity elements always have this property. For ten points, identify this general property which is held by a member x of a group if xx = x.
The number of elements in the free monoid described by this term is givenidentify this set of numbers of the form a + bı
idempotence [accept word forms]