# 4. Abstractions

{% content-ref url="abstractions/pre-class" %}
[pre-class](https://backend-course.cornellappdev.com/chapters/abstractions/pre-class)
{% endcontent-ref %}

{% content-ref url="abstractions/lecture" %}
[lecture](https://backend-course.cornellappdev.com/chapters/abstractions/lecture)
{% endcontent-ref %}

{% content-ref url="abstractions/demo" %}
[demo](https://backend-course.cornellappdev.com/chapters/abstractions/demo)
{% endcontent-ref %}

{% content-ref url="abstractions/handout" %}
[handout](https://backend-course.cornellappdev.com/chapters/abstractions/handout)
{% endcontent-ref %}

{% content-ref url="abstractions/api" %}
[api](https://backend-course.cornellappdev.com/chapters/abstractions/api)
{% endcontent-ref %}