FUNCTION:  MultPerm - multiply permutations,    
CALLING SEQUENCE:  MultPerm(w,P);,                   MultPerm(w,P,m);
    ,PARAMETERS:  w = a list of integers representing a group element
             P = a set (or list) of equations {s1=<perm1>,s2=<perm2>,...}
             m = the largest integer moved by the permutations (optional)
SYNOPSIS:   
  Let w be a list [i_1,i_2,...,i_l] of positive integers. Normally w will
  represent a product of generators in some Coxeter group.
  Let P be a set (or list) of equations {s1=<perm1>,s2=<perm2>,...},
  where each expression <perm_i> is a permutation of the integers 1,2,...
  in disjoint cycle format. For a description of this format, see
  group[permgroup]. 
  MultPerm(w,P) returns the product of the permutations s.i_1 ,..., s.i_l,
  using the convention that permutations act on the right. The result is
  expressed in disjoint cycle format, canonically arranged so that (1) the
  first listed element of each cycle is smallest, and (2) the cycles are
  ordered by increasing first elements. Fixed points are omitted. A third
  argument m, if present, indicates that the permutations involve only the
  integers 1,...,m.
  For any root system R, the second operand of PermRep(R) is a set of
  equations for the simple Reflections of W(R) that is compatible with the
  requirements for P. To convert from a permutation to a Reduced expression
  for the corresponding element of W(R), use the function Perm2Word.
EXAMPLES:   ,  P:={s1=[[6,7]],s2=[[7,8]]};
  MultPerm([1,2],P);                    yields            [[6,8,7]]
  MultPerm([2,1],P);                    yields            [[6,7,8]]
  P:=op(2,PermRep(D4)); w0:=LongestElt(D4);
  MultPerm(w0,P,8);                     yields    [[1,8],[2,7],[3,6],[4,5]]
    ,SEE ALSO:  Perm2Word, PermRep, group[permgroup]):
