<\body> The provides the following environments for computer algebra sessions: <\explain|> Environment for marking a session. All macros below are only for use inside sessions. <\explain|> An input field with a and the actual input. <\explain|> An output field. <\explain|> Fields with ordinary text. These may for instance be used for comments and explanations. <\explain|> This macro is used inside output fields for displaying error messages. In fact, these environments are based on environments of the form -session>, -input>, -output>, -textput> and -errput> for every individual language >. If language-specific environments do not exist, then , , , and are taken instead. It is recommended to base the language-specific environments on the generic ones, which may have different implementations according to the style ( the package). For this purpose, we also provide the environment, which is similar to , except that margins remain unaltered. <\initial> <\collection>