Equations for 23.trs

Equation 1

sel(from(cX), sel(0, :(cX,cY))) = sel(:(cX, from(s(cX))), cX)

Equation 2

:(0,from(0)) = from(:(0,x))

Equation 3

:(x,s(from(from(0)))) = :(s(sel(z,from(z))),0)