“…In fact, çarks can be thought of as Z-quotients of periodic rivers of Conway [5] or graphs dual to the coset diagrams of Mushtaq, [18]. As we shall see later in the paper, çarks provide a very nice reformulation of various concepts pertaining to indefinite binary quadratic forms, such as reduced forms and the reduction algorithm, ambiguous forms, reciprocal forms, the Markoff value of a form, etc.…”