Right most derivations for abab:
Case 1:
S → aSbS
→ aSb (applying S → π)
→ abSaSb (applying S → bSaS)
→ abSab (applying S → π)
→ abab (applying S → π)
Case 2:
S → aSbS
→ aSbaSbS (applying S → aSbS)
→ aSbaSb (applying S → π)
→ aSbab (applying S → π)
→ abab (applying S → π)