Let us construct the truth table of the following proposition.
f=((pβq)β§(qβr))β(pβr)
Β p00001111βq00110011βr01010101βpβq11110011βqβr11011101β(pβq)β§(qβr)11010001βpβr11110101βf11111111ββ
It follows that the formulaΒ ((pβq)β§(qβr))β(pβr)Β is a tautology.