of militarization of Sikhs under Guru Arjun's son Guru Hargobind. Guru Arjan Dev explained to the five Sikhs who accompanied him to Lahore, that Guru Hargobind has to build a defensive army to protect the people. Guru Hargobind trained in shashtar vidya, a form of martial arts that became prevalent among the Sikhs. He first conceptualized the idea of the kirpan through the notion of Sant Sipahi, or "saint soldiers". The relationship between the Sikhs and the Mughals further deteriorated following the execution of the ninth Guru Tegh Bahadur by Aurengzeb, who was highly intolerant of Sikhs, partially driven by his desire to impose Islamic law. Following the executions of their leaders and facing increasing persecution, the Sikhs officially adopted militarization for self-protection by creating later on the Khalsa; the executions also prompted formalization of various aspects of the Sikh faith. The tenth and final guru, Guru Gobind Singh formally included the kirpan as a mandatory article of faith for all baptised Sikhs, making it a duty for Sikhs to be able to defend the needy, suppressed ones, to defend righteousness and the freedom of expression. Legality In modern times there has been debate about allowing Sikhs to carry a kirpan that falls under prohibitions on bladed weapons, with some countries allowing Sikhs a dispensation. Other issues not strictly of legality arise, such as whether to allow carrying of kirpans on commercial aircraft or into areas where security is enforced. Belgium On 12 October 2009, the Antwerp court of appeal declared carrying a kirpan a religious symbol, overturning a €550 fine from a lower court for "carrying a freely accessible weapon without demonstrating a legitimate reason". Canada In most public places in Canada a kirpan is allowed, although there have been some court cases regarding carrying on school premises. In the 2006 Supreme Court of Canada decision of Multani v. Commission scolaire Marguerite‑Bourgeoys the court held that the banning of the kirpan in a school environment offended Canada's Charter of Rights and Freedoms, and that the restriction could not be upheld under s. 1 of the Charter, as per R. v. Oakes. The issue started when a 12-year-old schoolboy dropped a 20 cm (8-inch) long kirpan in school. School staff and parents were very concerned, and the student was required to attend school under police supervision until the court decision was reached. A student is allowed to have a kirpan