Kindergarten? They just took bra/kets, Feynman diagrams and substituted block-looking shapes. The underlying logic is hardly changed to kindergarten level.

Kindergarten? They just took bra/kets, Feynman diagrams and substituted block-looking shapes. The underlying logic is hardly changed to kindergarten level. The kid better have a masters in physics to follow this. "...i.e. we need to conjugate the first Hilbert space (although this gives an isomorphic copy). In the above argument establishing the bijection we used the matrix representation of Hilbert spaces and hence essentially the whole vector space structure, but in fact we need none of this, and we will show that in any picture calculus we always have..."