# ExtElement -- the class of all Ext-algebra elements

## Description

This type represents elements in Ext-algebras. Each object of type ExtAlgebra is itself a type E, and homogeneous elements in E belong also to the type ExtElement, which is the parent of E. Internally an element of type ExtElement is of type BasicList consisting of two basic lists, the first is a list of coefficients and the second is a list of indices for the generators occurring in the element.

 i1 : L = lieAlgebra{a,b}/{a a b,b b a} o1 = L o1 : LieAlgebra i2 : E = extAlgebra(5,L) o2 = E o2 : ExtAlgebra i3 : x = 4 ext_2 - ext_3 o3 = 4ext_2 - ext_3 o3 : E i4 : x#0 o4 = BasicList{4, -1} o4 : BasicList i5 : x#1 o5 = BasicList{2, 3} o5 : BasicList