Pattern of escalating exponents on D, E, F: complete DEF, DEF2, DE2F2, ____, D2E2F3 by identifying the leftward sweep of exponent increments to fill in the missing fourth term.

View each string as D^a E^b F^c, where omitted exponents equal 1. Exponents increase by +1 one letter at a time, cycling right-to-left.

• Term 1: D¹E¹F¹ (shown as DEF).
• Term 2: D¹E¹F² (increment F).
• Term 3: D¹E²F² (increment E).
• Term 4: D²E²F² (increment D) ⇒ missing term.
• Term 5: D²E²F³ (increment F again) — given.