R e l a t i o n a l R e a s o n i n g f o r M a r k o v C h a i n s i n a P r o b a b i l i s t i c G u a r d e d L a mb d a C a l c u l u s Alejandro Aguirre, Gilles Barthe, Lars Birkedal, Aleš Bizjak, Marco Gaboardi and Deepak Garg Imdea Software, Aarhus University, University at Buffalo SUNY, MPI-SWS
o n e - t i me p a d 1 0 1 1 0 1 0 1 message 1 1 0 1 0 0 1 1 key (uniformly sampled) 0 1 1 0 0 1 1 0 ciphertext K e y p r o p e r t y : p e r f e c t s e c r e c y
r e l a t i o n a l p r o p e r t i e s ● t w o e x e c u t i o n s o f t h e s a me o r d i f f e r e n t p r o g r a ms two executions ● o n e c o u l d c o mp u t e b o t h a n d c o mp a r e t h e m ● i s t h e r e a b e t t e r w a y t o r e a s o n ?
r e l a t i o n a l l o g i c
r e l a t i o n a l l o g i c ICFP’17
r e l a t i o n a l l o g i c ICFP’17
r e l a t i o n a l l o g i c ICFP’17 T wo terms
r e l a t i o n a l l o g i c ICFP’17 related by a property T wo terms
r e l a t i o n a l l o g i c ICFP’17 related by a property T wo terms
r e l a t i o n a l l o g i c How to express this exactly?
r e mi n d e r : p r o b a b i l i t y ( d i s c r e t e ) d i s t r i b u t i o n ma r g i n a l s f o r y x
c o u p l i n g s 1 0 1 ● l e t & i s a c o u p l i n g ● l e t U s e f u l c a s e s : & i s a R - c o u p l i n g & ( D e n o t e d )
e x a mp l e : c o i n fl i p ● S o me w a y s o f c o u p l i n g t w o f a i r c o i n s : H T H T H 1/2 0 H 1/4 1/4 equality product T 0 1/2 T 1/4 1/4 H T H T H 0 1/2 H p ½ - p inequality general T 1/2 0 T ½ - p p
f u n d a me n t a l l e mma I f i s a n R - c o u p l i n g o f a n d , I d e a : T o p r o v e a r e l a t i o n a l p r o p e r t y a b o u t d i s t r i b u t i o n s , w e “ s y n c r a n d o mn e s s ” t o b u i l d t h e a p p r o p r i a t e c o u p l i n g I n p a r t i c u l a r : ● ● ( s t o c h a s t i c d o mi n a n c e )
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 1 0 0 0
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 T h e r e f o r e ,
o n e - t i me p a d r e v i s i t e d 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 T h e r e f o r e , O n e c a n a l s o s h o w ,
( d i s c r e t e t i me ) ma r k o v c h a i n s ● d i s c r e t e s e t o f s t a t e s ● p r o b a b i l i s t i c t r a n s i t i o n f u n c t i o n S2 1/2 S1 1 1 1/2 S3
r e l a t i o n a l p r o p e r t i e s r e l a t e t w o M a r k o v c h a i n s o r t w o r u n s o f t h e s a me o n e ½ ⅓ ½ ½ ⅓ ⅓ ½ ⅔ ½ ⅔ ½ ⅔ 0 1 2 1 2 0 . . . . . . w h i c h o n e i s f a s t e r ?
e x a mp l e : s t o c h a s t i c d o mi n a n c e ½ ⅓ ½ ⅓ ½ ⅓ ½ ⅔ ½ ⅔ ½ ⅔ 1 2 1 2 0 0 . . . . . . 1/2 n n+1 1/2 m m+1
e x a mp l e : s t o c h a s t i c d o mi n a n c e ½ ⅓ ½ ⅓ ½ ⅓ ½ ⅔ ½ ⅔ ½ ⅔ 1 2 1 2 0 0 . . . . . . 1/2 1/6 n n n n+1 1/2 1/6 m m m+1 m+1
e x a mp l e : s t o c h a s t i c d o mi n a n c e ½ ⅓ ½ ⅓ ½ ⅓ ½ ⅔ ½ ⅔ ½ ⅔ 1 2 1 2 0 0 . . . . . . 1/2 1/6 1/3 n n n n n n+1 1/2 1/6 1/3 m m m m m+1 m+1
e x a mp l e : s t o c h a s t i c d o mi n a n c e ½ ⅓ ½ ⅓ ½ ⅓ ½ ⅔ ½ ⅔ ½ ⅔ 1 2 1 2 0 0 . . . . . . 1/2 1/6 1/3 n n n n n n+1 1/2 1/6 1/3 m m m m m+1 m+1
s o f a r ● P r o b a b i l i t i e s & M a r k o v c h a i n s a r e a u s e f u l mo d e l i n g t o o l ● S o me i n t e r e s t i n g p r o p e r t i e s a r e r e l a t i o n a l ● T h e s e c a n b e s t u d i e d w i t h c o u p l i n g s
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s . . .
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s . . . P r o b l e m : 1 ) N o t e x p r e s s i v e e n o u g h !
r e p r e s e n t i n g M a r k o v C h a i n s ● i n fi n i t e s e q u e n c e ( s t r e a m ) o f d i s t r i b u t i o n s . . . P r o b l e m : 1 ) N o t e x p r e s s i v e e n o u g h ! 2 ) P r o b a b i l i s t i c d e p e n d e n c e
r e p r e s e n t i n g M a r k o v C h a i n s ● a s d i s t r i b u t i o n s o v e r s t r e a ms . . . 0 1 2 1 2 1 0 . . . 0 -1 0 1 0 -1 -2 . . . -2 -3 -2 -3 -4 0 -1 . . .
r e p r e s e n t i n g M a r k o v C h a i n s ● a s d i s t r i b u t i o n s o v e r s t r e a ms . . . 0 1 2 1 2 1 0 . . . 0 -1 0 1 0 -1 -2 . . . -2 -3 -2 -3 -4 0 -1 . . .
r e p r e s e n t i n g M a r k o v C h a i n s ● a s d i s t r i b u t i o n s o v e r s t r e a ms . . . 0 1 2 1 2 1 0 . . . 0 -1 0 1 0 -1 -2 . . . -2 -3 -2 -3 -4 0 -1 . . . P r o b l e m : N o t d i s c r e t e !
t h e p r o b l e m w i t h s t r e a m d e fi n i t i o n s ● A s t r e a m i s p r o d u c t i v e i f i t o u t p u t s e v e r y fi n i t e p r e fi x i n fi n i t e t i me F o r i n s t a n c e , ● E x a mp l e o f n o n - p r o d u c t i v e s t r e a m:
g u a r d e d l a mb d a c a l c u l u s ● T e r ms : ● T y p e s : An element A stream now “later” [1] Clouston, R., Bizjak, A., Grathwohl, H.B., Birkedal, L.: The guarded lambda-calculus: Programming and reasoning with guarded recursion for coinductive types. ( LMCS ‘16 )
s t r e a ms i n g l c time 0 0 0 1 time 1 time 2 2 0 1 . . .
s t r e a ms i n g l c time 0 0 0 1 time 1 time 2 2 0 1 . . . All prefxes are discrete!
p r o b a b i l i s t i c g l c ● T e r ms : ● T y p e s :
s t r e a m d i s t r i b u t i o n s i n g l c time 0 0 1 2 time 1 0 1 1 0 0 2 time 2 0 1 2 0 2 1 . . .
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