... 1) ) c) (( n = k*(k - 1)/ 2 + j ) and (j = k) ==> (n = k*(k+ 1)/ 2 ) d) ( n = k*(k+ 1)/ 2 ) ==> ( (n = k*(k - 1)/ 2 + j ) and ( j = k) ) e) (( n = k - 1) and (j = k+ 1)) ==> ( j -n = -2 ) ... a) P(x,y,z) ( x > y ) or ( y > z ) . ≡ Xét P(1,2, 3), P(3,2, 1), P(3,-5, 7) b) P(x,y) ( 5 > x ) or ( 10 < y ) or not(x < y) . ≡ Xét P(5, 6) , P(10, 5) c) P(x,y) ( ( x=y ) ... (A or Y) e) (A ==> B) ==> X f) ( (not (A ==> X) and B ) ==> Y g) not (A or B) <==> ( (not A) and (not B) ) h) (A ==> X) ==> ( (not A) and X ) i) (X ==> Y)...