The Commens Dictionary
Quote from ‘A Syllabus of Certain Topics of Logic’
The System of Existential Graphs is a certain class of diagrams upon which it is permitted to operate certain transformations.
There is required a certain surface upon which it is practicable to scribe the diagrams and from which they can be erased in whole or in part.
The whole of this surface except certain parts which may be severed from it by “cuts” is termed the sheet of assertion.