Bochvar's Three-Valued Logic
This Demonstration presents a simple test for Bochvar's (1939) three-valued logic. The values are: True, False, and Undefined (or Paradoxical or Meaningless), with associated numerical values 1, 0, 1/2, respectively. The value of compound propositions is evaluated according to Bochvar's matrices for internal connectives.
A simple two-dimensional area is occupied by triangles, squares, and pentagons of three different sizes and two colors. If in a statement an individual constant with no reference appears ( in case of a world with two figures and ), then the statement is meaningless.
S. Haack, Deviant Logic, London: Cambridge University Press, 1974 p. 169.