Fan (machine) the airflow from the fans. Thus, fans may become ineffective at cooling the body if the surrounding air is near body temperature and contains high humidity. The punkah fan was used in India about 500 BCE. It was a handheld fan made from bamboo strips or other plant fibre, that could be rotated or fanned to move air. During British rule, the word came to be used by Anglo-Indians to mean a large swinging flat fan, fixed to the ceiling, and pulled by a servant, called the punkawallah. For purposes of air conditioning, the Han Dynasty craftsman and engineer Ding
Presentation of a group for generators and the Cayley table for relations. The negative solution to the word problem for groups states that there is a finite presentation for which there is no algorithm which, given two words "u", "v", decides whether "u" and "v" describe the same element in the group. This was shown by Pyotr Novikov in 1955 and a different proof was obtained by William Boone in 1958. Suppose "G" has presentation and "H" has presentation with "S" and "T" being disjoint. Then The deficiency of a finite presentation is just and the "deficiency" of a finitely presented group "G", denoted