from re import VERBOSE


def glu(pointer, main_stack, aux_stack):
    """
    Glu
    If the main stack is non-empty, duplicate the top element.
    """
    if VERBOSE:
        print("Glu", main_stack, aux_stack)
    if main_stack:
        main_stack.append(main_stack[-1])
    return(pointer, main_stack, aux_stack)