Based on the FA you already designed, your next task is to extend it to a Pushdown Automaton (PDA) which can recognise arithmetic expressions with brackets. All brackets must be paired up correctly. Multiplication operator can't be omitted. Some accepted examples: $1,-2,-(1),(1+2) *(3-7.3), 1 /(-3-1), 8^{*}-(3 / 8),((1.2)) /(2.1)$ Some rejected examples: (3)), (2)(3), $4-)($, (1.)5, ((3)3) In Appendix, we show you an example of PDA which accepts strings of unary numbers with correctly matched brackets. Please fully understand how it works. When you design your PDA, you should use your FA (from previous worksheet) as a start point. You need to modify your FA into a PDA, thinking carefully where are the positions you should allow open/close brackets. For full marks the diagram must be complete and correct in every respect.

Appendix - An Example of PDA A simple example of PDA is a recogniser for the language \[ \{1,11,111,(1),(1)(1),(1(11)),((1)(1) 11), \ldots \ldots\} \] Below is a possible PDA.

Task 2 - model answer Please use this as a start point for Portfolio task 3

Public Answer

EEBDD9 The First Answerer