1. $p→(p→p)$ (THEN-1)
2. $p→((p→p)→p)$ (THEN-1)
3. $(p→((p→p)→p))→((p→(p→p))→(p→p))$ (THEN-2)
4. $(p→(p→p))→(p→p)$ (MP from lines 2,3)
5. $(p→p)$ (MP from lines 1,4)
1. $p→(p→p)$ (THEN-1)
2. $p→((p→p)→p)$ (THEN-1)
3. $(p→((p→p)→p))→((p→(p→p))→(p→p))$ (THEN-2)
4. $(p→(p→p))→(p→p)$ (MP from lines 2,3)
5. $(p→p)$ (MP from lines 1,4)