What are the organic reactions that are taking place in this reaction?

I know that **A** is the product of a Knoevenagel condensation between the aldehyde and the diethyl malonate, due to the acidic protons of the latter, but I don't know what the reaction between that product and potassium cyanide would be.


[![enter image description here](https://i.stack.imgur.com/ZvoZz.png)](https://i.stack.imgur.com/ZvoZz.png)




Here is what I think is going on: 


1. $Step$ $1$: As the OP correctly identified is a Knoevenagel condensation to give A diethyl 4-cyclohexyl-benzalmalonate.
2. $Step$ $2$ is an example of little-used ester hydrolysis using cyanide ion to give initially the acyl cyanide which is unstable in aq EtOH and gives the diacid B
3. $Step$ $3$ is loss of one carboxy group by acid catalysed decarboxylation to give the cinnamic acid C
4. $Step$ $4$ formation of the mixed anhydride D
5. $Step$ $5$ cyclisation through formation of an aluminium-acyl complex [literature example here](http://orgsyn.org/demo.aspx?prep=CV2P0081) to give the final product 6-cyclohexyl-Inden-1-one E


[![enter image description here](https://i.stack.imgur.com/zR00R.png)](https://i.stack.imgur.com/zR00R.png)


 5

@Waylander has provided a well-reasoned solution to the post. I offer a different interpretation. Knoevenagel product **1a** has been converted in high yield to cyano ester **2a** and subsequently hydrolyzed to phenylsuccinic acid (**3a**) [1](http://orgsyn.org/Default.aspx). In the addition of cyanide to the double bond of **1a** and protonation, one of the labile ester groups is cleaved by cyanide. (e.g., Diethyl malonate is readily monosaponified by base in the cold.) Cyclization of anhydride **4a** has been accomplished by standard Friedel-Crafts methods but, like Waylander, I am a big fan of polyphosphoric acid (PPA). The cyclohexyl series **b** (R = *c*-C6H11) is likely to lead to ketoacid **5b**.   
  

[![enter image description here](https://i.stack.imgur.com/PQJvb.jpg)](https://i.stack.imgur.com/PQJvb.jpg)
  
  

1) C. F. H. Allen and H. B. Johnson, [*Organic Synthesis, Coll. Vol. 4*, 804, **1963**](http://orgsyn.org/Default.aspx).; Vol. *30*, 83, **1950**.


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