(b) Because of the sequence of values of the function g 1 (g 2 ), substituting a link of type 1 with a link of type 2 in a fixed P C n leads to an increase in the index. After this, one might think that this property suggests that when the number of links equal to two (X 2 ) increases then the index increases. However, this is generally not true, see the following examples written with the notation introduced in the paragraph below: