Gradient vertex color for proportional editing - Archived: Blender Development - Developer Forum
Proportional Edit — Blender Manual
Amazon.com: Blender 2.8X Introductory-Level Instructional Handout on How to Model and Animate a Sea Turtle: Proportional Editing and Parenting eBook : Samaniego MEd, Adriel: Kindle Store
How to use proportional editing in Blender - Artisticrender.com