function scr_84_pop()
{
    if (!variable_global_exists("chemg_stack"))
    {
        global.chemg_stack = array_create(0);
        global.chemg_stack[0] = 0;
    }
    var top_ndx = global.chemg_stack[0];
    if (top_ndx <= 0)
        show_error("stack empty", true);
    global.chemg_stack[0] = top_ndx - 1;
    return global.chemg_stack[top_ndx];
}