a ∧ ¬a |- b ∧ ¬b
1     a ∧ ¬a     assump 0
2     b |- a ∧ ¬a
2.1   b          assump 2
2.2  ¬b         ¬I 2.1
3     b ∧ ¬b    ∧I 2.1, 2.2
4    ¬b |- a ∧ ¬a
4.1  ¬b          assump 4
4.2   b         ¬E 4.1
5     b ∧ ¬b    ∧I 4.1, 4.2

0  a ∧ ¬a |- b ∧ ¬b
1         a ∧ ¬a       assump 0
2         b |- a ∧ ¬a
2.1         b          assump 2
2.2         a ∧ ¬a     reit 1
3        ¬b            ¬intro 2
4        ¬b |- a ∧ ¬a
4.1         ¬b         assump 4
4.2         a ∧ ¬a     reit 1
5        b             ¬elim 4  (RAA)
6        b ∧ ¬b        ∧intro 5,3