Availability:Arithmetic function (see is/2) 
[ISO]div(+IntExpr1, 
+IntExpr2)Integer division, defined as Result is (IntExpr1 - IntExpr1 mod IntExpr2) 
// IntExpr2. In other words, this is integer division that 
rounds towards -infinity. This function guarantees behaviour that is 
consistent with
mod/2, i.e., the 
following holds for every pair of integers
X,Y where Y =\= 0.
        Q is div(X, Y),
        M is mod(X, Y),
        X =:= Y*Q+M.