The canvas is not simply an inert place for the canvas items to exist. There is also a background context menu, giving access to the edit menu functionality such as cut/copy/paste, and also keyboard entry.
The following keystrokes insert an operation
+ |
add |
- |
subtract |
* |
multiply |
/ |
divide |
^ |
pow |
% |
percent operator |
& |
integral |
= |
Godley table |
@ |
plot |
# |
start a text comment, finish with return |
Typing any other character, then return will insert an operation (if the name matches), or otherwise a variable with that name.