GITBOOK-25: change request with no subject merged in GitBook

Author: Sarah Thiam Jia Hui

SUMMARY.md

@@ -7,7 +7,6 @@
 * [Key Concepts](key-concepts/README.md)
   * [Architecture](key-concepts/architecture.md)
   * [Subnets](key-concepts/subnets.md)
-  * [Checkpointing](key-concepts/checkpointing.md)
   * [Fees](key-concepts/fees.md)
 * [Reference](reference/README.md)
   * [Networks](reference/networks.md)

key-concepts/architecture.md

@@ -8,7 +8,7 @@ description: Architectural components in the IPC framework.
 
 ## Validator nodes
 
-Operators of a subnet run a full validator node for both the parent and the child subnet. Requiring the nodes of child subnets to run the nodes of parents is a security parameter to ensure [checkpointed](checkpointing.md) states of the subnet are appropriately stored, at the right time in the parent. 
+Operators of a subnet run a full validator node for both the parent and the child subnet. Requiring the nodes of child subnets to run the nodes of parents is a security parameter to ensure [checkpointed](broken-reference) states of the subnet are appropriately stored, at the right time in the parent. 
 
 The following components make up a node:
 
@@ -18,7 +18,7 @@ The following components make up a node:
 
 ### ABCI++
 
-The [ABCI++](https://members.delphidigital.io/learn/abci) interface is implemented in order to handle the IPC ledger logic and transaction handling, using the [Filecoin Virtual Machine](https://docs.filecoin.io/smart-contracts/fundamentals/the-fvm) (or Ethereum-compatible FVM). The ABCI can pass [checkpointed](checkpointing.md) headers to the parent and use the ledger to gather relevant signatures. 
+The [ABCI++](https://members.delphidigital.io/learn/abci) interface is implemented in order to handle the IPC ledger logic and transaction handling, using the [Filecoin Virtual Machine](https://docs.filecoin.io/smart-contracts/fundamentals/the-fvm) (or Ethereum-compatible FVM). The ABCI can pass [checkpointed](broken-reference) headers to the parent and use the ledger to gather relevant signatures. 
 
 An ABCI++ application can contact the [IPLD](https://docs.filecoin.io/basics/project-and-community/related-projects#ipld) [resolver & store](../reference/ipld-resolver.md) to read and write data so that it is IPLD addressable. 
 

key-concepts/checkpointing.md

@@ -20,7 +20,7 @@ Subnets within a single hierarchy tree have native communication protocols and a
 
 ## Checkpointing state
 
-To ensure security of a subnet, child subnets within a single hierarchy treee, periodically save snapshots of state to their parent subnet. This includes critical information (e.g. subnet state, membership information etc.). This is know as checkpointing and you can read more [here](checkpointing.md). 
+To ensure security of a subnet, child subnets within a single hierarchy treee, periodically save snapshots of state to their parent subnet. This includes critical information (e.g. subnet state, membership information etc.). This is know as checkpointing and you can read more [here](broken-reference). 
 
 ## Subnet usage