Rref is the inert form of rref.
Rref returns rref without evaluation. It is used in conjunction with mod in Maple syntax mode to find the row reduction to echelon form of a matrix with coefficients in ℤ/pℤ (see also 5.54.3).
Example, solve in ℤ/13ℤ
Input in Xcas mode :
you need to eval(ans()) to get :
and conclude that x=3%13 and y=3%13.
Input in Maple mode :