[ref] rename i subscript to n, to leave room for imaginary unit
[fix] correct display of trig. functions in MathJax/LaTeX
[rea] add some paragraph elements
[add] add illustrations
[rea] various text fixes
[add] complete section about reference wave
[ref] minor: expand css header selector up to h6
[add] write section for obj+ref combined
[ref] move stuff about complex calculation to a separate page