Compute: {{MATH_90}} {{CMD_91}} While it is not obvious at all, let us try the substitution {{MATH_92}} Then {{ENV_93}} and so {{ENV_94}} From here we now make the second (and more obvious) substitution {{MATH_95}} Then {{MATH_96}}, and {{ENV_97}} So {{ENV_98}} {{CMD_99}} {{CMD_100}} {{CMD_101}}