#define insert_constraint(sys,cnst) xbt_swag_insert(cnst,&(sys->constraint_set))
#define remove_variable(sys,var) do {xbt_swag_remove(var,&(sys->variable_set));\
xbt_swag_remove(var,&(sys->saturated_variable_set));} while(0)
#define insert_constraint(sys,cnst) xbt_swag_insert(cnst,&(sys->constraint_set))
#define remove_variable(sys,var) do {xbt_swag_remove(var,&(sys->variable_set));\
xbt_swag_remove(var,&(sys->saturated_variable_set));} while(0)