The primitive `lp_domain(Xs,L,U)` is provided for declaring domain variables for linear programming (LP) solvers. After the call, the domain of each of the variables in `Xs` is restricted to the range `L..U`, where `L` ( 0) and `U` are either integers or floats. If the domain of a variable is not declared, it is assumed to be in the range of .

The primitive `lp_integer(X)` notifies the LP solver that the variable `X` is of an integer type, and the primitive `lp_integers(Xs)` forces the list of variables `Xs` to be of an integer type. If the domain of an integer variable is not declared, then it is assumed to be in the range of 0..268435455.

Neng-Fa Zhou 2013-01-25