The plus sign (+) is a symbol used to show addition, and this book explains it very well. It covers adding things together; defines the plus sign as a symbol; shows how "plus" is sometimes replaced with the word "and;" defines a sum; shows addition problems constructed left to right and top to bottom; and shows the commutative property of addition (the sum is the same regardless of the order of the addends).
Super illustrations make this fun to read and memorable.
Keep this one on the shelf with "The Mission of Addition." The Mission of Addition (Math Is Categorical) Enjoy!