18 and 25 Feb 2004
CS 3243 - Logical Agents
26
Propositional logic: Semantics
nEach model specifies true/false for each proposition symbol
nE.g. P1,2  P2,2  P3,1
n false true false
n
nWith these symbols, 8 possible models, can be enumerated automatically.
nRules for evaluating truth with respect to a model m:
n ØS is true iff S is false 
n S1 Ù S2   is true iff S1 is true and S2 is true
n S1 Ú S2   is true iff S1is true or S2 is true
n S1 Þ S2  is true iff S1 is false or S2 is true
n i.e., is false iff S1 is true and S2 is false
n S1 Û S2 is true iff S1ÞS2 is true andS2ÞS1 is true
n
nSimple recursive process evaluates an arbitrary sentence, e.g.,
n
nØP1,2 Ù (P2,2 Ú P3,1) = true Ù (true Ú false) =  true Ù true = true