##
## The next instruction is the allocation to coxeter_wgraphs of the list of
## the W-graphs of the preceding cells. Each W-graph is printed out as a list
## of pairs, one for each node in the corresponding cell. Each pair is of
## the form [descent set,edge-list] where the descent set is the list of
## descent generators for the corresponding node (in the case of one-sided
## cells) or again a pair [left descent set, right descent set], in the
## case of twosided cells; the edge-list is a list of pairs [dest,mu], where
## mu is the mu-coefficient of the edge, and dest is the destination vertex,
## written here as a single number, viz. its index in the cell for the
## priviously printed enumeration of the cells (recall taht in GAP list
## indices start with 1, not 0.) This is different from the representation of 
## W-graphs used in Chevie; Chevie writes down the mu-coefficients as a full 
## NxN matrix, where N is the size of the cell, whereas we use a sparse 
## representation.
##
