Lect7 - Unifier A unifier (also substitution, binding...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
A unifier (also substitution , binding list* ) is a set of pairings of variables with terms: {v 1 = e 1 , v 2 = e 2 , v 3 = e 3 , … v n = e n } such that each variable is paired at most once • a variable’s pairing term may not contain the variable directly or indirectly Unifier {x = Socrates} * Do not confuse with bound / free variables!!! 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Most General Unifier MGU The MGU imposes the fewest constraints, specifying the weakest conditions for matching MGU is unique order is not important variable names are not important (alphabetic variants) Applying the MGU to an expression yields a most general unification instance . Variable substitutions are always interpreted with the unifier applied 2
Background image of page 2
What is the MGU? M(Ann,x,Bob) M(Ann,x,Bob) M(Ann,x,Bob) M(y,x,Chuck) M(Ann,x,Bob) M(y,x,Father-of(Chuck)) P(w,w,Fred) P(x,y,y) Q(r,r) Q(x,F(x)) Q(r,r) Q(x,F(y)) R(G(x,Bob),y,y) R(z,G(Fred,w),z) 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Negation and Quantifiers   x P(x)   x P(x)   x P(x)   x P(x) x P(x)   y Q(y)   x y [P(x) Q(y)] x y [P(x) Q(y)]   y x [P(x) Q(y)] (also , also all ’s) BUT x y P(x,y) is NOT the same as y x P(x,y) 4
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/13/2011 for the course CS 440 taught by Professor Levinson,s during the Fall '08 term at University of Illinois, Urbana Champaign.

Page1 / 14

Lect7 - Unifier A unifier (also substitution, binding...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online