Update erc20.md

advanced_knowledge/token_standards/erc20.md

@@ -2,59 +2,53 @@
 
 <br>
 
-* The ERC20 standard defines a common interface for contracts implementing this token, such that any compatible token can be accessed and used in the same way. 
+* defines a common interface for contracts implementing this token, such that any compatible token can be accessed and used in the same way.
+* a transaction sending ether to an address changes the state of an address. a transaction transferring a token to an address only changes the state of the token contract, not the state of the recipient address.
+* one of the main reasons for the success of EIP-20 tokens is in the interplay between `approve` and `transferFrom`, which allows for tokens to not 
+only be transferred between externally owned accounts (EOA).
+   - but to be used in other contracts under application specific conditions by abstracting away `msg.sender` as the mechanism for token access control.
+*  a limiting factor lies from the fact that the EIP-20 `approve` function is defined in terms of `msg.sender`. 
+    - this means that user’s initial action involving EIP-20 tokens must be performed by an EOA. 
+    - if the user needs to interact with a smart contract, then they need to make 2 transactions (`approve` and the smart contract internal call `transferFrom`), with gas costs.
 
 <br>
 
-### ERC20-compliant token contract
-
-* totalSupply
-Returns the total units of this token that currently exist. ERC20 tokens can have a fixed or a variable supply.
-
-* balanceOf
-Given an address, returns the token balance of that address.
 
-* transfer
-Given an address and amount, transfers that amount of tokens to that address, from the balance of the address that executed the transfer.
-
-* transferFrom
-Given a sender, recipient, and amount, transfers tokens from one account to another. Used in combination with approve.
-
-* approve
-Given a recipient address and amount, authorizes that address to execute several transfers up to that amount, from the account that issued the approval.
+---
 
-* allowance
-Given an owner address and a spender address, returns the remaining amount that the spender is approved to withdraw from the owner.
+### ERC20-compliant token contract
 
-* Transfer
-Event triggered upon a successful transfer (call to transfer or transferFrom) (even for zero-value transfers).
+<br>
 
-* Approval
-Event logged upon a successful call to approve.
+* `totalSupply`: Returns the total units of this token that currently exist. ERC20 tokens can have a fixed or a variable supply.
+* `balanceOf`: Given an address, returns the token balance of that address.
+* `transfer`: Given an address and amount, transfers that amount of tokens to that address, from the balance of the address that executed the transfer.
+* `transferFrom`: Given a sender, recipient, and amount, transfers tokens from one account to another. Used in combination with approve.
+* `approve`: given a recipient address and amount, authorizes that address to execute several transfers up to that amount, from the account that issued the approval.
+* `allowance`: given an owner address and a spender address, returns the remaining amount that the spender is approved to withdraw from the owner.
+* `Transfer`: event triggered upon a successful transfer (call to transfer or transferFrom) (even for zero-value transfers).
+* `Approval`: event logged upon a successful call to approve.
 
 <br>
 
 ---
 
 ### ERC20 optional functions
 
-In addition to the required functions listed in the previous section, the following optional functions are also defined by the standard:
-
-* name
-Returns the human-readable name (e.g., "US Dollars") of the token.
-
-* symbol
-Returns a human-readable symbol (e.g., "USD") for the token.
+<br>
 
-* decimals
-Returns the number of decimals used to divide token amounts. For example, if decimals is 2, then the token amount is divided by 100 to get its user representation.
+* in addition to the required functions listed in the previous section, the following optional functions are also defined by the standard:
+     - `name`: returns the human-readable name (e.g., "US Dollars") of the token.
+     - `symbol`: returns a human-readable symbol (e.g., "USD") for the token.
+     - `decimals`: returns the number of decimals used to divide token amounts. For example, if decimals is 2, then the token amount is divided by 100 to get its user representation.
 
 <br>
 
 ---
 
-### The ERC20 interface defined in Solidity
+### the ERC20 interface
 
+<br>
 
 ```
 contract ERC20 {