0 :: a
eq :: a → a → c
false :: c
fork :: b → a → b → b
if :: c → c → c → c
lt :: a → a → c
member :: a → b → c
null :: b
s :: a → a
true :: c
lt(s(X), s(Y)) → lt(X, Y)
lt(0, s(U)) → true
lt(V, 0) → false
eq(W, W) → true
eq(s(P), 0) → false
eq(0, s(X1)) → false
member(Y1, null) → false
member(U1, fork(V1, W1, P1)) → if(lt(U1, W1), member(U1, V1), if(eq(U1, W1), true, member(U1, P1)))