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(1) (p«-*q) a (r <-* s) —* (p v r <->■ q v s)

33 :: (7)=>75

76. (p<-*<?) - [(r 4-5) -* [(p -» r) 4- (q - .*)]]

Dowód. 16 :: 13=>16 p/q, <//p=>( 1)

(1)    (p*-*q)-> [(P-* r)-*($-> r)]

32 :: (1)=>(2)

(2)    (p*->q) a (p-*r)-(g-r)

39 :: (2) =>12 p/r, q/s=>{3)

(3)    [(p «-*g) a (p —* r)] a (r «-*s) -*• (q -► r) a (r -* .v)

32    :: 16 p/q, ^/r, r/s=>(4)

(4)    (q -* r) a (r -> s) -►(</-► s)

16 :: (3) =>(4) =>(5)

(5)    [(p q) a (p -> r)] a (r «-* .v) — (q-> s)

38    :: 34 p/r «-> s, ą!p -> r => (6)

(6) (p<-+q) a [(r«-*s) a (p —♦ r)] —♦ (p «-♦ q) a [(p -> r) a (r <-♦ s)]

16 :: 40 p/p*-*q, qfr*-+s, r/p -* r => (6) => (7)

(7)    [(p<-<7) a (r «-♦ .v)] a (p —* r) —* (p q) a £(p —* r) a (r4-*.v)]

16 :: (7) =-41 p/p+-+q, q/p->r, r/r .v ==> (8)

(8) [(p*-*q) a (r4-*s)] a (p —* r) —* [(p *-* q) a (p —* r)] a (r4-».v)

16 :: (8) =>(5) =>(9)

(9)    [(p <-*'/) a (r 4-4 .%•)] a (p —* r) —* (q —* s)

33    :: (9) =>(10)

(10)    (p «-* q) a (r s) -* [(p -* r) -> ((/ -♦ s)]

39    :: 56 =>56 p/r, q/s=>{\\)

(11)    (p4-> q) a (r 5) —»{q 4-» p) a (.<?4-* r)

16 :: (11) =>(10) pfq, qfp. rfs, .v/r=>(12)

(12)    (p*-+q) a (r^.v) -* [(q -* s) -► (p -* r)]

16 :: (10) => 14 p/p -*■ r, q/q -> s =>(13)