tests: Equality on addresses, slices, cells (#1279)

* Semantics tests for equality on addresses, slices, cells

* feat(docs): equality of `myAddress()` and `contractAddress(initOf CurrentContract())`

And small updates of similar descriptions on the Operators page of the
Book

* Tests of equality of slices with references to cells

* Tests of equality of cells manually built using builders (with cells having references and without)

---------

Co-authored-by: Novus Nota <[email protected]>

docs/src/content/docs/book/expressions.mdx

@@ -246,7 +246,7 @@ contract ExampleContract {
 
 ## `initOf`
 
-Expression `initOf{:tact}` computes initial state (`StateInit{:tact}`) of a [contract](/book/contracts):
+Expression `initOf{:tact}` computes initial state, i.e. `StateInit{:tact}` of a [contract](/book/contracts):
 
 ```tact
 //                     argument values for the init() function of the contract
@@ -263,13 +263,32 @@ initOf ExampleContract(
 );
 ```
 
-Where `StateInit{:tact}` is a built-in [Struct][s], that consists of:
+The `StateInit{:tact}` is a built-in [Struct][s], that consists of:
 
 Field  | Type               | Description
 :----- | :----------------- | :----------
 `code` | [`Cell{:tact}`][cell] | initial code of the [contract](/book/contracts) (the compiled bytecode)
 `data` | [`Cell{:tact}`][cell] | initial data of the [contract](/book/contracts) (arguments of `init(){:tact}` function of the contract)
 
+:::note
+
+  For workchain $0$, the [`Address{:tact}`][p] of the current contract obtained by calling the [`myAddress(){:tact}`](/ref/core-common#myaddress) function is identical to the one that can be obtained by calling the [`contractAddress(){:tact}`](/ref/core-common#contractaddress) function with the initial state of the current contract computed via `initOf{:tact}`:
+
+  ```tact {6}
+  contract TheKingPrawn {
+      receive("keeping the address") {
+          let myAddr1 = myAddress();
+          let myAddr2 = contractAddress(initOf TheKingPrawn());
+
+          myAddr1 == myAddr2; // true
+      }
+  }
+  ```
+
+  However, if you only need the address of the current contract at runtime and not its `StateInit{:tact}`, use the [`myAddress(){:tact}`](/ref/core-common#myaddress) function, as it consumes **significantly** less gas.
+
+:::
+
 [p]: /book/types#primitive-types
 [cell]: /book/cells#cells
 [s]: /book/structs-and-messages#structs

docs/src/content/docs/book/operators.mdx

@@ -220,7 +220,7 @@ two / 1; // 2
 
 :::note
 
-  Note that the following relationship between the division and modulo operators always holds for `Int{:tact}` type:
+  The following relationship between the division and [modulo](#binary-modulo) operators always holds for `Int{:tact}` type:
 
   ```tact
   a / b * b + a % b == a; // true for any Int values of `a` and `b`,
@@ -247,12 +247,24 @@ two % 1; // 1
 -1 % -5; // -1
 ```
 
-The simplest way to avoid confusion between the two is to prefer using positive values via [`abs(x: Int){:tact}`](/ref/core-math#abs):
+The simplest way to avoid confusing getting the modulo with getting the remainder is to [use only unsigned integers](/book/security-best-practices#misuse-of-signed-integers). Alternatively, consider using [`abs(){:tact}`](/ref/core-math#abs) function to ensure non-negative values:
 
 ```tact
 abs(-1) % abs(-5); // 1
 ```
 
+:::note
+
+  The following relationship between the [division](#binary-divide) and modulo operators always holds for `Int{:tact}` type:
+
+  ```tact
+  a / b * b + a % b == a; // true for any Int values of `a` and `b`,
+                          //   except when `b` is equal to 0 and we divide `a` by 0,
+                          //   which is an attempt to divide by zero resulting in an error
+  ```
+
+:::
+
 :::note
 
   Did you know, that in JavaScript `%{:tact}` works as a _remainder_ operator, but not _modulo_ operator (like in Tact)?\