def _mutl_by_int(expr, val):
    """ Create an expression that multiply an expression by an integer
    Args:
        expr: Expression to constrain
        val:  Integer value to multiply expression with
    Returns:
        New expression
    """
    if val == 1:
        return expr
    if val == -1:
        return -expr
    if val == 0:
        return 0
    return val * expr