The algorithm used for eseq builds up a path on 1..n by appending extra edges on to the path on
nodes 1..(n-2).
The function eseqa constructs paths on 1..n using an alternative algorithm. For odd n, the tour starts at 1,
then takes steps of size 1,2,..m repeatedly, where m is (n-1)/2, For even n, the path constructed
is formed as eseqa(n+1), followed by dropping node n+1.
The function kntour\_drop removes instances of n from the tour, creating an open approximately eulerian path on the complete graph with n-1 nodes.
The function kntour\_add inserts an extra node n+1 into a tour
on nodes 1, ..n. It adds a detour to the tour visiting all edges joining nodes 1..n to n+1. The result is an open approximately eulerian path on the complete graph with n+1 nodes.