Task A $[0\mathrm{.}4$ Points$]$: front page of the answersheet.

Carl Clumsy noticed $($alas too late$)$ that he accidentally pushed a negative number into a Stack that was originally meant to store only positive numbers. Now the un$-$wanted negative number, which should not be there, is at the $3$rd position of the Stack underneath two positive numbers. He asks his

friend Clementine Clever what to do: she replies that he must use another additional Stack to solve this problem. To give Carl Clumsy an additional helpful hint, Clementine Clever presents one algebraic term which describes precisely, with mathematical rigour, the combination of operations on both Stacks up to the point at which the un$-$wanted negative number appears visibly on the Top of the first Stack.

PRESENT this algebraic term $($which Clementine Clever had shown to Carl Clumsy$)$ on the front page of your homework sheet.