-- POPEMPTYproof Derivation of pop(empty) ~ empty Applying the axiom resp. theorem empty = (new,0) at positions [1],[0,0] of the preceding formula leads to pop((new,0)) ~ (new,0) Simplifying the preceding formula leads to pop(new,0) ~ (new,0) Applying the axiom resp. theorem pop(f,i) = (f,pred(i)) at position [0] of the preceding formula leads to (new,pred(0)) ~ (new,0) Applying the axiom resp. theorem pred(0) = 0 at position [0,1] of the preceding formula leads to (new,0) ~ (new,0) Simplifying the preceding formula leads to True Number of proof steps: 5 Solutions: True