Continuing from Note6, as branch-points are moved by varying parameters
let an associated system of cuts be moved with them.
Now assume that there are two branch-points such that a suitable
parameter variation causes them to merge to become one branch-point.
Use a system of cuts in which they are adjacent. On merging the cut
joining them ceases to exist. Take a circle centred on the joint limit
and so small that only the two which are to merge enter it. For each
other cut take a fixed contour avoiding the circle and crossing that
cut only. If the non-merging branch-points move under the parameter
variation the contour has also to be kept ctear of their tracks. This
is a detail which is left to the reader. Then as explained near the
beginning following the contour from initial point back to initial
point gives a permutation on branches which is assigned to that
cut. So under merging of two branch-points the surviving cuts retain
their associated permutations.
Note that if the original system of cuts was standard the derived
system will also be standard since the number of branch-points and the
number of cuts are both reduced by one.