Canelina has learned to play any music piece on the piano by ear - brain with both hands or feet

It is easy.


First the melody is learned by trial and error.


The the bass is learned by trial and error . It is much more difficult but the good news is that the notes are just 7, 12 of the scale is not known, so Canelina can even try in random 7 notes until she finds the right one that goes correctly with the melody.


Then the 3rd and 5th are added for harmony.


Some chords contain the more refined intervals of 6th, 7th, 9th etc. but with most of the the 3rd is taken too.


An example song.


Imagine - John Lennon


Bass is C. Right hand is derived from 1,3,5. So the notes are C, E, G. In fact the right hand plays E,G  C,  E,G  C  E,G,B  C


Then bass is F. The 1,3,5 rule gives F A C. In fact the right hand uses these notes but plays them with the least change from C,E,G. So it plays F,A C  F,A C.


And so it goes.


Reference:


Bach bass rules:
http://normanschmidt.net/scores/bachjs-general_bass_rules.pdf