1. It appears that the display default for sin, cos etc is unambiguous.
Therefore you could just instruct the users of the meaning of sin x y.
2. If you require parentheses, how about defining two functions, psin(x) and
pcos(x). Just before you display a step, replace sin by psin, cos by pcos.
Define the TeX properties of psin and pcos so they display as \sin and
\cos.
RJF
> Instead of generating cos xy for some input or the other,
> we could avoid the ambiguity by writing some custom code to
> process sin, cos, etc for TeX output, which would put in
> extra parentheses in some cases.
>
>