E to f are semitones, in the law of twelve averages. The octave is divided into 12 minutes, and every two adjacent tones are semitones, such as C and bD, #D and E, so EF is semitone, and E to #4 can't say that, but E to #F are full tones and E to F are semitones. Raising f to #F will increase a semitone, so it will increase two semitones. EF is actually a rule, just like, why is 2 higher than 1, for example, octave, and the vibration frequency of treble is just twice that of bass, so the two sounds are very similar, so the names are the same!

You may even ask, why don't you add a black keys between EF? The total number of * * * is twelve semitones, but there are only 1 1 keys in it, and one of them is single, and the two sides are balanced, which is not mentioned in the music theory book, so you should regard it as a rule!