D.4.3 glpk errors

Possible error messages are

     <'bad glpk specification'>

which means that the input did not conform to the description given above, and

     <'memory overflow'>

It is not considered an exceptional condition for no feasible solution to exist, and in that case an empty list is returned.

The glpk documentation gives no assurance as to the correctness of reported solutions, so the user should also take the possibility of incorrect results into account.