Changes

#<math>\land</math>: <math>\varphi \land \psi \vdash \psi \land \varphi</math><!--

#<math>\land</math>: <math>(\varphi \land \psi) \land \delta \vdash \varphi \land (\psi \land \delta)</math>test#<math>\alpha \vdash \alpha \land \alpha</math>#<math>\alpha \land \beta, \gamma \land \delta \vdash \gamma \land \beta</math>