Rule of Replacement ·AssumeΦ(A)is a proposition formula containing a logical expression A Tautologies (B)is another proposition formula obtained from (A)by replacing all occurrences of A play a with B important role to inference and proving IfB≡A,then(A)≡中(B)Rule of Replacement • Assume 𝛷(𝐴) is a proposition formula containing a logical expression 𝐴 Tautologies play a important role to inference and proving If 𝑩 ≡ 𝑨, then 𝜱(𝑨) ≡ 𝜱(𝑩) • 𝛷(𝐵) is another proposition formula obtained from 𝛷(𝐴) by replacing all occurrences of 𝐴 with 𝐵