Round Squares Are No Contradictions (Tutorial on Negation Contradiction and Opposition) (2015), p. 51
by Beziau, Jean-Yves

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Caption

Duality between contrary and subcontrary negations in modal logic

Logic

Aristotelian family

Béziau Sigma-4

Boolean complexity

4

Number of labels per vertex (at most)

1

Errors in the diagram

Yes

Geometry

Shape

Octagon (irregular)

Colinearity range

0

Coplanarity range

0

Cospatiality range

0

Representation of contradiction

By central symmetry

Vertex description

Conceptual info

No

Mnemonic support (AEIO, purpurea ...)

No

Form

none

Label type

symbolic

Symbolic field

logic

Contains partial formulas or symbols

No

Logical system

modal logic

Edge description

Style

Diagram is colored

Yes

Diagram is embellished

No

Additional notes

The relation between $\Box p$ and $\neg p$ should be in blue (contrary) instead of green (subcontrary). The relation between $\Diamond p$ and $\neg p$ should be in blue (contrary) instead of green (subcontrary).