Existential graph

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An existential graph is a type of diagrammatic or visual notation for logical expressions,
proposed by Charles Sanders Peirce, who wrote on graphical logic as early as 1882,[2]
and continued to develop the method until his death in 1914.

Peirce proposed three systems of existential graphs:

alpha, isomorphic to sentential logic and the two-element Boolean algebra;
beta, isomorphic to first-order logic with identity, with all formulas closed;
gamma, (nearly) isomorphic to normal modal logic.

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A logical graph is a special type of diagrammatic structure in
any one of several systems of graphical syntax that
Charles Sanders Peirce developed for logic.

In his papers on qualitative logic, entitative graphs, and existential graphs,
Peirce developed several versions of a graphical formalism,
or a graph-theoretic formal language, designed to be interpreted for logic.

In the century since Peirce initiated this line of development,
a variety of formal systems have branched out from what is
abstractly the same formal base of graph-theoretic structures.