\ Converted from Example 2 of http://lpsolve.sourceforge.net/5.5/Xpress-format.htm
Minimize
 obj: -2 x3
Subject To
 c1: +x2 -x1 <= 10
 c2: +x3 +x2 +x1 <= 20
Bounds
 x3 >= 2
 x3 <= 3
 x1 >= 2.1
 x1 <= 30
General
 x3 x1
Semi-continuous
 x3 x1
End