1. An information processing apparatus for processing an input signal to determine an output signal for a system having a plurality of system variables, the input signal having a plurality of variables including at least one variable with an unknown value defining an unbounded variable and at least one variable with a known value defining a bounded variable, the unbounded variable defining uncertainty for the input signal, the variables in the system constrained by a plurality of predetermined rules, the rules including predetermined combinations of a plurality of system variables, the information processing system comprising: an addressable memory having stored therein a binary representation of the rules constraining the variables in the system; proposition storage memory having stored therein a binary representation indicating which rules define a relationship for a variable; scanning means for receiving the input signal, and for scanning the proposition storage memory to identify all rules which define a relationship for a variable; logic means for addressing the respective identified rules in the addressable memory and determining from the input signal and the rules all of the bounded system variables for a given input signal by determining which variables have the same bounded value in all of the identified rules.