introduce "lab groups"

Author: afeld

labs/lab_04.md

@@ -20,6 +20,7 @@ We will be practicing [pair programming](../docs/pairing.md) and [documentation-
 ### Setup
 
 1. Pair up with someone who isn't on your [project team](../docs/project.md#teams).
+   - This will be known as your "Lab group". Subsequent Labs will use the same people, repository, and dataset.
 1. Pick a dataset that has unique identifiers for each row.
    - You can use a dataset from one of your [projects](../docs/project.md), or [pick a different one](https://python-public-policy.afeld.me/en/columbia/assignments/open_ended.html#open-data-portals).
    - You'll use a CSV as the data source to power your API.

labs/lab_05.md

@@ -38,7 +38,7 @@ Seeing projects with `<name>2.py`. Splitting code up into smaller files will hel
 
 ## Steps
 
-You'll [pair](../docs/pairing.md) in your group, repository, and dataset from [Lab 4](lab_04.md). Work on branches and submit pull requests for the chunks of work — you decide what the "chunks" are.
+You'll [pair](../docs/pairing.md) in your Lab group. Work on branches and submit pull requests for the chunks of work — you decide what the "chunks" are.
 
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labs/lab_07.md

@@ -13,7 +13,7 @@ Can use the CLI for DuckDB (and other databases):
 
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-You'll [pair](../docs/pairing.md) in your group, repository, and dataset from Labs [4](lab_04.md) and [5](lab_05.md). Work on branches and submit pull requests for the chunks of work — you decide what the "chunks" are.
+You'll [pair](../docs/pairing.md) in your Lab group. Work on branches and submit pull requests for the chunks of work — you decide what the "chunks" are.
 
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