# Not Only Barbara (2015), p. 99

by Dekker, Paul

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- Aristotelian family
- Classical Sigma-2
- Boolean complexity
- 3
- Number of labels per vertex (at most)
- 1
- Uniqueness of the vertices up to logical equivalence
- Yes
- Errors in the diagram
- No
- Shape
- Square (regular)
- Colinearity range
- 0
- Coplanarity range
- 0
- Cospatiality range
- 0
- Representation of contradiction
- By some other geometric feature

### Logic

### Geometry

- Conceptual info
- No
- Mnemonic support (AEIO, purpurea ...)
- Yes
- Form
- none
- Label type
- symbolic
- Symbolic field
- logic
- Contains partial formulas or symbols
- No
- Logical system
- syllogistics
- Contains definitions of relations
- No
- Form
- solid lines
- Has arrowheads
- No
- Overlap
- No
- Curved
- No
- Hooked
- No
- As wide as vertices
- No
- Contains text
- No
- Label type
- none

### Vertex description

### Edge description

- Diagram is colored
- No
- Diagram is embellished
- No
- Tags
- subject negation

### Style

### Additional notes

- This is a twisted square of opposition: the two contradiction relations are not on the diagonals of the diagram, but on the vertical edges.

AäB = A'eB = $\forall x(\neg Ax \to \neg Bx)$

AxB = A'aB = $\forall x(\neg Ax \to Bx)$

AöB = A'iB = $\exists x(\neg Ax \wedge Bx)$

AyB = A'oB = $\exists x(\neg Ax \wedge \neg Bx)$

(Cf. p. 99.)