Left: disease 疒 (An ice- 冫-cold building 广 makes sick.), right: past tense identifier, to fulfill 了 (The still arm-less 了 child 子 should be completed.)
Mnemonic
Turning the disease into 'history', means: treatment. - Or: The disease of the arm-less 了 child 子, shall be treated.
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!