[Help-glpk] Subject to two conditions

[João Vilela]

Dear all,

I'm solving a variation of a max flow problem in a graph, where:

set V, default {1..n};        /* is a set of nodes */
set E, within V cross V;     /* is a set of arcs */
set L, within E cross E;      /* is a set to map edges to edges */
var x2{(i,j) in E}, binary;    /* x2[i,j] indicates whether there is any 
flow going through link (i,j) */

And I have the following condition:

> s.t. condition{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] <=0) or 
(sum{(i,j,i1,j1) in L} x2[i1,j1] >= 2);

Basically, this means that I need the sum of those x2[i1,j1] to be 
different from 1 (i.e. less or equal to 0 *or* bigger or equal than 2). 
Although, this code gives me the following error:

"operand preceding <= has invalid type"

Any idea?

Thank you,
Joao