Left: half 半 (A cake 二 with candles 丷 is cut by knife丨into half), right: knife 刂. (Think of a hanko (= name stamp): a wooden stick that is cut in half to create a face into which the name characters are carved.
Mnemonic
Cut in half and engraved with a knife to make: a stamp.
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!
